Tawakel Karman, who heads the rights group Women Journalists Without Chains, was stopped by plain-clothes police in a main street as she was heading home with her husband, according to rights activists who declined to be identified on Sunday..
The reason for her arrest was unclear, but she is being held in Sanaa's main prison, according to her family.
A security official said the arrest stemmed from a warrant issued by prosecutors, without specifying.
Karman, a member of the central committee of the Islamist Al-Islah (Reform) party, has been involved in Sanaa demonstrations in support of a popular revolt in Tunisia that have been marked by calls for political change in Yemen.
On Saturday, hundreds of Sanaa University students held duelling protests on campus, with some calling for Yemeni President Ali Abdullah Saleh to step down and others for him to remain in office.
Saleh, who has been in power for decades, was re-elected in September 2006 for a seven-year mandate.
A draft amendment of the constitution, under discussion in parliament despite opposition protests, could further stretch his tenure by allowing a life-long mandate.