Heat the oil in a large pot over medium heat. Add the onion, celery, carrots, garlic, and mushrooms, then sauté until they are tender, about 10 min. Season with salt and pepper. Meanwhile, peel and dice the potatoes; dice the beef cubes into small pieces (about 1 cm).
Add the barley, potatoes, and beef, then sauté 2 min with stirring. Pour in the broth. Bring to a boil, then reduce the heat, cover and simmer 50 min, or until the barley and potatoes are tender, stirring occasionally.