Jonathan Waknine, a resident of Valley Village near Los Angeles, had been cited Tuesday afternoon after another demonstrator at the encampment at Justin Herman Plaza reported that he had a gun, police spokesman Sgt. Daryl Fong said.
Officers found an unloaded semi-automatic pistol holstered to Waknine's right hip and cited him for possession of a concealed firearm, Fong said.
After being released, Waknine allegedly approached a ranger from the city's Recreation and Park Department at about 8:30 a.m. Wednesday and confronted him about Tuesday's incident, according to Fong.
He told the ranger that the gun was registered to him and that police were wrong in taking it, Fong said.
The ranger, who was doing a daily site inspection of the encampment, said he was unfamiliar with the case.
Waknine then allegedly told the ranger that he had an AK-47 assault rifle at home and said he was going to bring it to the camp loaded the next day, Fong said.
The ranger alerted police, who went to the camp, found Waknine and arrested him at about 2 p.m.
He was booked into jail on suspicion of making felony making threats against a public employee, Fong said.
The arrest was Wednesday's second at the encampment.
Earlier in the day, a Pennsylvania man was arrested for throwing a glass bottle at a Department of Public Works employee cleaning the bocce ball courts in the plaza, police said.
Despite the recent problems, Mayor Ed Lee has said there are no immediate plans to remove the encampment.