Plainclothes policemen arrested Nagorik Oikya convener Mahmudur Rahman Manna from a house in capital's Banani area early Tuesday.
Manna's wife Meher Nigar alleged that Detective Branch of police picked up her husband from his niece Shahnama Sharmin's house.
Shahnama Sharmin, niece of Manna, said, plainclothes police introducing them as DB arrested his uncle around 3:30am where he went into hiding since his phone conversations.
But DB police denied detention of Manna by them.
However, Dhaka Metropolitan Police's Joint Commissioner Monirul Islam also said, they did not detain or arrest Manna.
The arrest came a day after the leak of his two controversial phone conversations.
Manna is a former Awami League leader, who quit the party to form his own organisation.