The detentions followed the arrest on Monday of another prominent activist campaigning for the independence of Western Sahara, a former Spanish colony annexed by Morocco in 1975.
Earlier this month a Moroccan court handed down sentences of up to eight years in prison to 12 independence-seekers convicted on charges of criminal association, vandalism, resisting arrest and participation in an armed crowd.
Sources said 50 people were injured when police cracked down on demonstrations in Western Sahara's largest city El Ayoun in May, but Moroccan authorities have said they moved on criminals.
Last year, Morocco rejected a UN-backed plan to resolve the dispute over the territory by granting autonomy to the region for five years and thereafter hold a referendum on self-rule.
The Polisario Front, which has been fighting against Moroccan rule for three decades, approved of the plan drafted by former US secretary of state James Baker.