This Veterans Employment Toolkit states:
A person who is active duty is in the military full time. They work for the military full time, may live on a military base, and can be deployed at any time. Persons in the Reserve or National Guard are not full-time active duty military personnel, although they can be deployed at any time should the need arise.
However, you may have received orders to serve active duty and some portion of your earnings are active duty pay.
A Leave and Earnings Statement (LES) will indicate how much you were paid. Your Reserve Unit may be able to tell you how much you were paid for active duty and Reserve duty.
State income tax codes may define issues differently for a specific state tax benefit. Is there a particular issue that you are referring to?