China arrests over coup rumours
The State Internet Information Office said the rumours had a "very bad influence on the public".
The office said 16 websites had been closed down for carrying the posts.
A spokesman for the office told state news agency Xinhua that a number of other people had been "admonished or educated".
He added some staff had been "criticised and punished accordingly" at China's biggest microblogging website Sina Weibo, where some of the rumours had circulated.
The web-postings came at a crucial time for China's ruling elite, which was hit by its biggest scandal in years when high-flying party official Bo Xilai was removed from his post.
Later in the year he had been expected to rise to the Politburo's Standing Committee, the Communist Party's main decision-making body.
Mr Bo's demise came amid allegations that his police chief and main political ally had tried to seek asylum at a US mission.