The number includes two people arrested after a clash between Saudi police and alleged al-Qaeda insurgents on Friday which left six insurgents and one policeman dead.
The Saudi interior ministry said 27 men were arrested for "suspicious activities" in May in a series of raids across the country; in the capital, Riyadh, Mecca and in the Eastern province and northern border.
Of these men, two were Somali, one Ethiopian and the rest Saudi nationals.
In addition, four people, an Iraqi and three Saudis, were detained in a June raid on a desert camp in Hafer al-Baten, which borders Iraq.
Nine other Saudis were arrested on suspicion of "being involved in terrorism", also in Hafer al-Baten, officials said.
News of the arrests came after Friday's clash in a residential area of Riyadh.
The interior ministry said security forces came under fire while pursuing seven alleged al-Qaeda suspects in the al-Nakhil district.
Saudi police killed six of the insurgents, whom the authorities say were planning attacks, and wounded a seventh. A Saudi policeman also died in the clash.
Weapons, ammunition, money, and forged documents, along with communication equipment and forged number plates were also found in the hideout, the authorities said.
Members of al-Qaeda have been blamed for a wave of deadly attacks in the kingdom since May 2003.
King Abdullah pledged in April to annihilate al-Qaeda-linked insurgents.
The country has been under pressure to crack down on militancy since the attacks on the US in September 2001. Fifteen of the 19 aircraft hijackers were said to be Saudi, but at least four of those named by the FBI may have been victims of identity theft.