Police in Nigeria’s capital Abuja have released members and leaders of the pressure group, Bring Back Our Girls, after holding them for several hours.
Many of those who were taken into custody are women, including former World Bank Vice-President Oby Ezekwesili.
The activists were rounded up into police vans as they marched to the presidential palace to put pressure on the government to ensure the release of the remaining Chibok schoolgirls.
One of the group’s leaders told the BBC that they were shocked by the police action, which they say violates democratic principles. They have vowed to continue their campaign.
A police statement says the activists were taken into custody to ensure there was no breakdown of law and order during their protests.
The Bring Back Our Girls campaign started after the mass abduction of nearly 300 schoolgirls in Nigeria’s north-eastern town of Chibok by Boko Haram militants in 2014.
The campaign gained international support including from Michelle Obama – the wife of the former US President Barack Obama.
Many of the schoolgirls have been released in a prisoner swap deal with Boko Haram, but there are still more than 100 who are still in the hands of the militants.