"K.T. Naveen Kumar was taken into custody by a Special Investigation Team (SIT) of the Karnataka Police for questioning," SIT Investigating Officer M.N. Anucheth told IANS here.
Kumar hails from Birur town in Chikkamagaluru district, about 250km west from here, Anucheth said.
Gauri Lankesh, a journalist known for her anti-establishment views and withering criticism of the Sangh parivar's brand of Hindutva, was shot dead by unidentified assailants on September 5 last year.
The killing had led to national outrage and protests by several groups over "rising intolerance" in the country and attempts to muzzle dissent with the criticism targeted at the Modi government and right wing groups.
The state government had set up the SIT to probe the journalist-activist's killing.
Editor of the well-known Kannada weekly Gauri Lankesh Patrike, Gauri, 55, was shot at the entrance of her home in Rajarajeshwari Nagar in the western suburbs of Bangalore after she appeared to have got off her car.
Her body was left sprawled at the doorway to her home. Gauri was shot in the forehead and chest.
A former correspondent with Sunday, a weekly magazine that used to be published by the ABP Group, Gauri was the eldest daughter of P. Lankesh, whose Lankesh Patrike had earned a reputation for being anti-establishment.
Gauri later started her own weekly. She courted trouble with an article against BJP leaders and was sentenced to six months in jail in a defamation case filed by Dharwad Lok Sabha MP Pralhad Joshi and party leader Umesh Dushi. But she escaped prison time as the court granted her bail and allowed her to appeal.
(With additional inputs from The Telegraph Calcutta and IANS)