Heat olive oil in a large pot or Dutch oven over medium-high heat. Add the beef cubes and brown them on all sides. Remove beef from the pot and set aside.
Add the chopped onion, carrots, and celery to the pot. Cook, stirring occasionally, until softened, about 5-7 minutes.
Return the browned beef to the pot. Stir in the rinsed barley, beef broth, thyme, and rosemary.
Bring the soup to a boil, then reduce the heat to low, cover, and simmer for 1.5 to 2 hours, or until the beef is tender and the barley is cooked through. Stir occasionally.
Season with salt and pepper to taste. If using, stir in the frozen peas during the last 5 minutes of cooking.
Ladle the soup into bowls and serve hot.
Notes
This soup can be made ahead of time and stored in the refrigerator for up to 3 days. It also freezes well.