The suspended Washington Wizards star arrived at D.C. Superior Court after 2 p.m. Friday and did not answer any questions from media.
The charge, which carries a maximum penalty of five years in prison, was filed Thursday in an "information," a document that indicates Arenas has reached a plea deal with prosecutors.
Arenas has acknowledged keeping unloaded guns in his locker at the Verizon Center. He says he took the guns out of the locker Dec. 21 in a "misguided effort to play a joke" on a teammate.
He has publicly employed the "goof ball" defense. He says he wasn't aware of the law, meant no harm and never takes anything seriously.