In a large resealable plastic bag, combine the flour, salt and 1/4 teaspoon pepper. Add beef and shake to coat. In a Dutch oven, brown beef in oil over medium heat. Remove and set aside.
In the same pan, saute mushrooms until tender. Add the broth, carrots, garlic powder, thyme and remaining pepper; bring to a boil. Add barley and beef. Reduce heat; cover and simmer for 20-25 minutes until the meat, vegetables and barley are tender.