The man was seen on Massachusetts Avenue and detained by Secret Service officers stationed near the residence on Wednesday following an intelligence bulletin from Texas, the Metropolitan Police Department said in a statement.
Harris and her husband have not moved in yet because of renovations to the home in Northwest DC near the US Naval Observatory. She's staying at Blair House, a guest home for the White House.
Metropolitan police said Paul Murray of San Antonio was held on charges that he carried a large-capacity ammunition-feeding device, a dangerous weapon, a rifle and unregistered ammunition.
No one was injured. The Secret Service referred questions to the Metropolitan Police.
It wasn't clear if Murray had an attorney who could comment on the charges against him.