The arrests follow the killing in shootouts of five police officers and two neighbourhood patrol guards last week. Police also discovered and defused three car bombs in Riyadh.
Security forces seized three vehicles packed with thousands of kilograms of explosives, including one they had been searching for since February, a ministry official said on Sunday, quoted by the state SPA news agency.
"Eight people linked with these incidents have been captured, but the investigation requires not revealing their identities and the roles they played," he said.
Saudi Arabia is battling a surge in violence believed to be linked to Usama bin Ladin's al-Qaida network.
The country issued a list of 26 most-wanted suspects, which has gone down to 22 since it was issued in December, after a series of human bombing attacks targeting residential compounds killed 52 people in May and November 2003.