Saudi secret police arrested Matruk Al Faleh, a political science university professor, on Monday after he criticised a prison where two other Saudi activists are serving jail terms, Human Rights Watch said in a statement.
"Saudi Arabia's arrest of ... Faleh confirms that human rights advocacy in that country remains a risky business," said Joe Stork, deputy director at Human Rights Watch's Middle East division. "By suppressing peaceful dissent, Saudi Arabia only stands to gain further notoriety as an abuser of human rights."
Faleh's family has not been told why he was arrested or if he had been charged, it said.
Interior Ministry spokesman Turki Al Mansour could not be reached for comment.
