The sites allegedly spread false rumors about troops deployed on the streets of the capital, which a spokesman for the State Internet Information Office said had caused "a very bad influence on the public."
The agency told the official state-run Xinhua news service that six people had been detained for failing to stop the rumors from spreading.
It could not be determined from independent sources if the reports of soldiers on the move in Beijing were actually true.
The government has been particularly sensitive to rumors of trouble in Beijing since the recent ouster of Bo Xilai has head of the Communist Party in the city of Chongquing. The New York Times said Bo's abrupt dismissal sparked rumors that a coup was a possibility.
The Times noted that bloggers and Web sites such as the ones shut down this weekend had also caused friction with the government last summer after two high-speed passenger trains collided.
China experts told the newspaper that Beijing's interest in snuffing out so-called rumors on the Internet was actually a means of stifling criticism of the government. "The whole idea of rumors and interest in accuracy is a ruse," said David Bandurski of the China Media Project at Hong Kong University. "It's a moniker for control."