Edmund Abu, the head of the Native Consortium for Research and Development, was detained in the early hours of Tuesday morning as he headed to the protest venue, sources said.
The protest was called in response to the government’s decision to raise pump prices of petrol, kerosene and diesel.
The Ministry of Trade made the announcement on Friday July 13, which was followed by the hike in transport fares.
Officials said the move was necessitated by developments at the international market.
The NCRD has been the most vocal against the move.
Mr Abu had threatened to stage a protest if the government failed to reverse the decision.
According to reports, the police have denied detaining him.
A police spokesman was quoted saying the activist was only called in for interrogation over his unapproved request for a permit to stage his protest.
There have been calls for his release by pro-democracy groups.
In a separate development, business in Freetown was partially disrupted on Tuesday due to a sit-down strike by junior staffers of the two government-owned commercial banks – the Sierra Leone Commercial Bank and the Rokel Commercial Bank.
The headquarters and all the branches of the two banks across the country were shut down for the day.
The aggrieved staffers, under the banner of the Junior Staff Association, are protesting the government’s decision to replace the banks’ existing system of emoluments with just a month’s salary as leave allowance.
They say they receive a meagre sum as salary and they feel disadvantaged by the new arrangement.
The changes were occasioned by the revised 2018 Budget passed by parliament last week.
The Supplementary Appropriation Bill, presented to Parliament by Finance Minister Jacob Jusu Saffa, reflected the ‘New Direction’ agenda of new President Julius Maada Bio.