The Gulf Center for Human Rights says 22 people were taken into custody Monday during a demonstration to demand the release of at least nine activists detained this month.
The group's statement Tuesday says those in custody include poets, writers and social media activists.
Oman has been hit this month by strikes in its oil industry. Last year, protests inspired by the Arab Spring called for a greater political openness.
In response, Oman's ruler Sultan Qaboos gave more powers to a council which until then had been advisory.