Preheat oven to 350 F. In a large saucepan over medium heat, melt butter. Whisk in flour and cook for a minute to brown. Pour in milk, chicken broth, salt, pepper and mixed frozen vegetables.
Continue to cook, while whisking constantly until thickened. Add in cooked and diced chicken and let heat through. Pour mixture into a large greased baking dish.
Place biscuits evenly on top of mixture. Bake for 25-30 minutes.