Oakland television station KTVU reports firefighters who arrived at the scene Sunday to check on the man saw he was armed and called police.
The officers who responded ordered him to drop the gun but officials say the man did not comply and officers fired and struck him.
Officers treated the man at the scene but he died from his injuries. Officials say they also recovered a gun from the scene.
Oakland police, Internal Affairs, and the district attorney's office are investigating.
Information from: KTVU-TV.