Among those held was Pu Zhiqiang, a prominent free-speech lawyer, who has represented many dissidents, including artist Ai Weiwei, and an activist of the "New Citizens' Movement", a group that urges Chinese leaders to disclose their assets. He was held on a charge of "causing a disturbance", two lawyers said.
He has also opposed the system of forced labour camps, which the government has abolished, and featured prominently in state media for that campaign.
Also detained were dissident Liu Di and Xu Youyu, a professor with the Chinese Academy of Social Sciences, a government think-tank, rights lawyer Shang Baojun said.
Shang said he did not know what charge Liu and Xu would face as the families have not received their detention notices.
Dissident Hu Shigen and Hao Jian, who teaches at the Beijing Film Academy, were also detained, according to Chinese Human Rights Defenders, a China-based rights advocacy group.
The detentions raised the stakes in a crackdown on dissent and underscored the sensitivity of Chinese leaders to criticism ahead of the 25th anniversary of the crushing of demonstrations around Tiananmen Square in Beijing on June 4, 1989.
"Pu is very influential and has a following in the mainstream audience," said Maya Wang of the New York-based advocacy group Human Rights Watch.