Bring 1 1/2 cups water to a boil in a medium saucepan; add barley. Cover, reduce heat, and simmer 18 minutes or until liquid is absorbed and the barley is tender. Drain and rinse under cold water; drain well.
While the barley cooks, combine feta cheese, tomatoes, peppers, basil, capers, vinegar, olive oil, garlic, and navy beans in a large bowl; toss well. Add the cooked barley; toss gently until combined. Serve immediately.