A ministry spokesman said on Tuesday in a statement the four policemen were killed by "machine-gun" fire in separate attacks on the road linking Riyadh and Qasim, northwest of the capital.
The attacks were carried out by "members of a deviant minority," the spokesman said.
Saudi authorities often refer to suspected Islamist sympathisers of Saudi-born Usama bin Ladin's al-Qaida network as a "deviant group" that has strayed from the right path.
On combing the region, security authorities "seized two car
bombs ready to be used as well as a third car containing arms," the spokesman added.
The district of Qasim around the town of Buraydah lies 320kms from Riyadh.