One Saudi policeman was killed and three others were wounded in clashes with militants in a town northeast of Riyadh.
A number of suspects were arrested in the battles, officials said.
Two police patrols checking a report that armed suspects were in a house in al-Baradah, 250 miles northeast of Riyadh, were fired on by suspects in a vehicle as they approached the house.
A later search of the house revealed large amounts of explosives and weapons. An unspecified number of suspects were arrested after the shooting. No more details were available.
Al-Arabiya TV reported that one of the three wounded police officers was in critical condition.
The region has been a site of frequent attacks linked to al-Qaida in Saudi Arabia. In April, four security officers were killed when a group of militants opened fire on a checkpoint in the region.