It is a crime in certain states to be arrested for possessing a gun without a license. If it happened in the US, it would be called a felony, not a misdemeanor. So what is the difference between a “felony” and a “misdemeanor”? It depends on the state.
The difference between a misdemeanor and a felony is that the latter is punishable by up to six months in jail and the former is punishable by up to three years in jail. If you are arrested for a felony you can never be tried or convicted, you can only apply for a restraining order that may delay but does not prevent the arrest.