diff --git a/src/libraries/System.Runtime/tests/System.Threading.Tasks.Tests/MethodCoverage.cs b/src/libraries/System.Runtime/tests/System.Threading.Tasks.Tests/MethodCoverage.cs
index 695cd6abb1714..579662f96dc1f 100644
--- a/src/libraries/System.Runtime/tests/System.Threading.Tasks.Tests/MethodCoverage.cs
+++ b/src/libraries/System.Runtime/tests/System.Threading.Tasks.Tests/MethodCoverage.cs
@@ -295,6 +295,7 @@ public static async Task Task_WhenAny_TwoTasks_WakesOnFirstCompletion()
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/99500", TestPlatforms.Browser)]
         public static void CancellationTokenRegitration()
         {
             ManualResetEvent mre = new ManualResetEvent(false);
@@ -312,6 +313,7 @@ public static void CancellationTokenRegitration()
         /// verify that the taskawaiter.UnsafeOnCompleted is invoked
         /// </summary>
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/99500", TestPlatforms.Browser)]
         public static void TaskAwaiter()
         {
             ManualResetEvent mre = new ManualResetEvent(false);
diff --git a/src/libraries/System.Runtime/tests/System.Threading.Tasks.Tests/Task/AsyncEnumerableToBlockingEnumerableTests.cs b/src/libraries/System.Runtime/tests/System.Threading.Tasks.Tests/Task/AsyncEnumerableToBlockingEnumerableTests.cs
index 0692aedb514f9..048025c5c947a 100644
--- a/src/libraries/System.Runtime/tests/System.Threading.Tasks.Tests/Task/AsyncEnumerableToBlockingEnumerableTests.cs
+++ b/src/libraries/System.Runtime/tests/System.Threading.Tasks.Tests/Task/AsyncEnumerableToBlockingEnumerableTests.cs
@@ -70,6 +70,7 @@ static async IAsyncEnumerable<int> CreateSourceEnumerable()
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/99519", TestPlatforms.Browser)]
         public static void AsyncEnumerableWithDelays()
         {
             var source = new InstrumentedAsyncEnumerable<int>(CreateSourceEnumerable());
@@ -104,6 +105,7 @@ static async IAsyncEnumerable<int> CreateSourceEnumerable()
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/99519", TestPlatforms.Browser)]
         public static void AsyncEnumerableWithException()
         {
             var source = new InstrumentedAsyncEnumerable<int>(CreateSourceEnumerable());
@@ -132,6 +134,7 @@ static async IAsyncEnumerable<int> CreateSourceEnumerable()
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/99519", TestPlatforms.Browser)]
         public static void AsyncEnumerableWithCancellation()
         {
             var source = new InstrumentedAsyncEnumerable<string>(CreateSourceEnumerable());
diff --git a/src/libraries/System.Runtime/tests/System.Threading.Tasks.Tests/Task/TaskContinueWithTests.cs b/src/libraries/System.Runtime/tests/System.Threading.Tasks.Tests/Task/TaskContinueWithTests.cs
index 2800a5e9e24c4..4cb9d47ca4ec8 100644
--- a/src/libraries/System.Runtime/tests/System.Threading.Tasks.Tests/Task/TaskContinueWithTests.cs
+++ b/src/libraries/System.Runtime/tests/System.Threading.Tasks.Tests/Task/TaskContinueWithTests.cs
@@ -1076,6 +1076,7 @@ public static void RunContinuationCancelTest_State()
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/99519", TestPlatforms.Browser)]
         public static void TestNoDeadlockOnContinueWith()
         {
             Debug.WriteLine("TestNoDeadlockOnContinueWith:  shouldn't deadlock if it passes.");
@@ -1255,6 +1256,7 @@ public static void LongContinuationChain_Unwrap_DoesNotStackOverflow()
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/99519", TestPlatforms.Browser)]
         public static void LongContinuationChain_Await_DoesNotStackOverflow()
         {
             const int DiveDepth = 12_000;
diff --git a/src/libraries/System.Threading/tests/MutexTests.cs b/src/libraries/System.Threading/tests/MutexTests.cs
index 6b06baeb76034..6d769c4297fae 100644
--- a/src/libraries/System.Threading/tests/MutexTests.cs
+++ b/src/libraries/System.Threading/tests/MutexTests.cs
@@ -661,6 +661,7 @@ private static void IncrementValueInFileNTimes(Mutex mutex, string fileName, int
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/96191", TestPlatforms.Browser)]
         public void NamedMutex_ThreadExitDisposeRaceTest()
         {
             var mutexName = Guid.NewGuid().ToString("N");
diff --git a/src/libraries/System.Threading/tests/SemaphoreSlimTests.cs b/src/libraries/System.Threading/tests/SemaphoreSlimTests.cs
index 7aabd01c39f1e..faac4d9cf9f85 100644
--- a/src/libraries/System.Threading/tests/SemaphoreSlimTests.cs
+++ b/src/libraries/System.Threading/tests/SemaphoreSlimTests.cs
@@ -90,6 +90,7 @@ public static void RunSemaphoreSlimTest1_WaitAsync()
         }
 
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/99519", TestPlatforms.Browser)]
         public static void RunSemaphoreSlimTest1_WaitAsync_NegativeCases()
         {
             // Invalid timeout