Forum for Democratic Change (FDC) Presidential Flagbearer Patrick Oboi Amuriat has been arrested.
He had been taken out of his car into a waiting police vehicle and driven away to a yet to be identified place.
It is believed he will be driven to Kyambogo nomination centre.
Police has banned processions and rallies but Amuriat insisted on moving with over 2,000 supporters.
Police responded by sealing off Najjanankumbi FDC head offices to prevent the procession.