During the protest, another man in plain clothes, who identifies himself as a police officer, also pulls out a pistol and fires two shots into the air near the stadium, where Argentina were playing Bosnia- Herzegovina.
Government spokesman Pedro Dantas said there had been no reports of anyone suffering gunshot injuries.
The incident took place at around the start of the group match between Argentina and Bosnia-Herzegovina, the first World Cup finals game to be played in the Maracana stadium since 1950.
Earlier, officers had fired stun grenades and tear gas to block a march by about 200 protesters heading towards the stadium.
A stand-off ensued, with demonstrators holding banners massing near a police line guarding the route to Maracana. The Protesters chanted "Fifa, go back to Switzerland".