The three-time All-Star insisted the guns were unloaded when he took them out of his Verizon Center locker on December 21.
"I had kept the four unloaded handguns in my house in Virginia, but then moved them over to my locker at the Verizon Center to keep them away from my young kids," Arenas said in a statement released to the media on Monday.
Arenas said he believed it was legal to store the guns in the District of Columbia. He said he took the guns out of his locker "in a misguided effort to play a joke on a teammate."
"Joke or not, I now recognize that what I did was a mistake and was wrong," he said.
"I should not have brought the guns to DC in the first place, and I now realize that there's no such thing as joking around when it comes to guns - even if unloaded."
No charges have been filed against Arenas, a nine-year National Basketball Association veteran who is averaging 22.7 points a game this season.
(Writing by Steve Ginsburg; Editing by Eric Walsh)