Under federal law, an air gun is not classed as a firearm, because it uses no explosive charge to expel a projectile. However, many states do regulate air rifles in some way, depending on factors like the owner's age and the rifle’s power. Individual county laws or ordinances may also apply. The only way to be sure is to check with your local administration. Different rules apply to hunting with air guns (rather than target shooting), so you need to check that with your state's game and fish authority.