diff --git a/src/transformers/training_args.py b/src/transformers/training_args.py
index a7b2ba0db3a7..bfd5b08da121 100644
--- a/src/transformers/training_args.py
+++ b/src/transformers/training_args.py
@@ -228,7 +228,7 @@ class TrainingArguments:
     command line.
 
     Parameters:
-        output_dir (`str`):
+        output_dir (`str`, *optional*, defaults to `"trainer_output"`):
             The output directory where the model predictions and checkpoints will be written.
         overwrite_output_dir (`bool`, *optional*, defaults to `False`):
             If `True`, overwrite the content of the output directory. Use this to continue training if `output_dir`
@@ -813,8 +813,11 @@ class TrainingArguments:
     """
 
     framework = "pt"
-    output_dir: str = field(
-        metadata={"help": "The output directory where the model predictions and checkpoints will be written."},
+    output_dir: Optional[str] = field(
+        default=None,
+        metadata={
+            "help": "The output directory where the model predictions and checkpoints will be written. Defaults to 'trainer_output' if not provided."
+        },
     )
     overwrite_output_dir: bool = field(
         default=False,
@@ -1547,6 +1550,14 @@ class TrainingArguments:
     )
 
     def __post_init__(self):
+        # Set default output_dir if not provided
+        if self.output_dir is None:
+            self.output_dir = "trainer_output"
+            logger.info(
+                "No output directory specified, defaulting to 'trainer_output'. "
+                "To change this behavior, specify --output_dir when creating TrainingArguments."
+            )
+
         # Parse in args that could be `dict` sent in from the CLI as a string
         for field in _VALID_DICT_FIELDS:
             passed_value = getattr(self, field)
diff --git a/tests/test_training_args.py b/tests/test_training_args.py
new file mode 100644
index 000000000000..7b1daabe1634
--- /dev/null
+++ b/tests/test_training_args.py
@@ -0,0 +1,42 @@
+import os
+import tempfile
+import unittest
+
+from transformers import TrainingArguments
+
+
+class TestTrainingArguments(unittest.TestCase):
+    def test_default_output_dir(self):
+        """Test that output_dir defaults to 'tmp_trainer' when not specified."""
+        args = TrainingArguments(output_dir=None)
+        self.assertEqual(args.output_dir, "tmp_trainer")
+
+    def test_custom_output_dir(self):
+        """Test that output_dir is respected when specified."""
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            args = TrainingArguments(output_dir=tmp_dir)
+            self.assertEqual(args.output_dir, tmp_dir)
+
+    def test_output_dir_creation(self):
+        """Test that output_dir is created only when needed."""
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            output_dir = os.path.join(tmp_dir, "test_output")
+
+            # Directory should not exist before creating args
+            self.assertFalse(os.path.exists(output_dir))
+
+            # Create args with save_strategy="no" - should not create directory
+            args = TrainingArguments(
+                output_dir=output_dir,
+                do_train=True,
+                save_strategy="no",
+                report_to=None,
+            )
+            self.assertFalse(os.path.exists(output_dir))
+
+            # Now set save_strategy="steps" - should create directory when needed
+            args.save_strategy = "steps"
+            args.save_steps = 1
+            self.assertFalse(os.path.exists(output_dir))  # Still shouldn't exist
+
+            # Directory should be created when actually needed (e.g. in Trainer)