Yeah, it is:
ART. 94. MUTINY OR SEDITION
(a) Any person subject to this chapter who--
(1) with intent to usurp or override lawful military authority, refuses, in concert with any other person, to obey orders or otherwise do his duty or creates any violence or disturbance is guilty of mutiny;
(2) with intent to cause the overthrow or destruction of lawful civil authority, creates, in concert with any other person, revolt, violence, or disturbance against that authority is guilty of sedition;
(3) fails to do his utmost to prevent and suppress a mutiny or sedition being committed in his presence, or fails to take all reasonable means to inform his superior commissioned officer or commanding officer of a mutiny or sedition which he knows or has reason to believe is taking place, is guilty of a failure to suppress or report a mutiny or sedition.
(b) A person who is found guilty of attempted mutiny, mutiny, sedition, or failure to suppress or report a mutiny or sedition shall be punished by death or such other punishment as a court-martial may direct.
Nah, it is not.
The Captain is questioning, the legal qualification of Obama to be President. This is not mutiny, nor is it sedition. If the person in question is not legally qualified to hold the office, then all subsequent actions are illegal.