Turkey had been seeking his extradition for an attack on a bank in Ankara in 1995.
The man, believed to be a member of Turkey's outlawed Marxist Revolutionary People's Liberation Party Front (DHKP-C), was arrested in Mestre, a port on the Adriatic Sea close to Venice, Agi said.
He is also accused of acting as a recruiter for DHKP-C, considered a terrorist group by Turkey, the European Union and the United States.
The Italian authorities must now decide on whether to allow his extradition to Turkey.
A bloody hostage standoff between the radical DHKP-C group and security forces left a top Istanbul prosecutor dead on Tuesday.
A day later, an armed woman linked to DHKP-C was killed by police as she tried to storm the city's police headquarters.
The Turkish authorities have rounded up over 30 suspected members of the organization since then.