A group of Saudis protested outside the Interior Ministry in Riyadh on Sunday to demand the release of jailed relatives, amid a heavy police presence.
The protest, involving dozens of men in traditional white robes and red headdresses, was the third such gathering in a week. The men were demanding the release of imprisoned relatives.
Saudi Arabia, which practices the puritanical Wahhabi school of Islam and has no elected parliament, has warned that protests will not be tolerated, as they violate the Koran's teachings, Reuters reports.
Saudi King Abdullah last week promised billions in handouts for Saudi citizens, new hospitals and medical centers and more jobs, and he pledged to set up an anti-corruption agency.
But reform activists responded with disappointment Friday.
"I feel disappointed, to say the least," one Saudi activist told CNN. "I do believe after these decrees, instead of sweeping reforms, they'll start sweeping up the activists. I'm afraid there will be a crackdown on activists here."
A "Day of Rage" organized online last week by Saudi activists hoping to emulate the uprisings in other parts of the Arab world, did not go ahead due to increased security.
On Sunday, at least 50 police cars surrounded the Interior Ministry.
"We have seen at least three or four police vehicles taking people away," an activist told Reuters. "Security have arrested around 15 people. They tried to go into the ministry to go and ask for the freedom of their loved ones."