Police seized Ratna Singh and three lawyers in a car, surrounded by at least 25 officers, on Saturday morning, according to a video released by the Cockroach Janta Party.
Earlier that day, officers visited Singh's house but were told she was not present.
When questioned, the officers claimed they had orders from higher authorities, yet no written notice was presented.
The detention comes amid heightened security in New Delhi ahead of the CJP's 'Jantar Mantar 2.0' protest, which seeks the resignation of Chief Election Commissioner Gyanesh Kumar amid allegations of manipulating voter lists.
The party has issued guidelines for participants, including restrictions on protest routes and the requirement to wear protective gear.
CJP has scheduled a protest for Sunday, with organizers warning police to respect protest rights.