A ministry official said in a statement carried by the Saudi Press Agency that the man had been caught during a raid on a neighbourhood of the Saudi capital.
Security sources later said the man was not a Saudi national but that he spoke Arabic. They did not give his nationality.
The statement said police had been hunting down members of the "deviant faction" - referring to al Qaeda militants - when they found the arms, which included rocket propelled grenade launchers, blocks of explosive material and hand grenades.