In a large bowl, combine the muffin mix and brown sugar. Combine the egg and milk; stir into dry ingredients just until moistened. Fold in blueberries.
Coat muffin cups with cooking spray or use paper liners. Fill half full with batter. Bake at 400° for 12-15 minutes or until a toothpick inserted in muffin comes out clean. Cool for 5 minutes before removing from pan to a wire rack. Serve warm.