Italian authorities began tracking the movement of the individuals after coming across online conversations of an extremist nature.
The number under investigation was put at 20 by leading daily Corriere della Sera, although other Italian press reports put the number at ten.
The Italian-born men are second generation immigrants aged between 20 and 30, Corriere said. Based in Rome and northern Italy, they were reportedly radicalized online and in places of worship.
The men have for months been traced by the special operations wing of the Italian police (Ros) working alongside Rome prosecutors.
Despite having links to extremists in Europe and the Middle East, the individuals are described as “lone wolves” and are not thought to have the capacity to carry out terrorist attacks.
Investigations in northern Italy uncovered recruiters from the Balkans and North Africa operating on behalf of terrorist groups, Corriere said.
The reports come as Rob Wainwright, head of the EU’s law enforcement agency Europol, said up to 5,000 Europeans have joined such groups as “foreign fighters”.
The majority are young men who could return to Europe to carry out attacks, Wainwright told British MPs on Tuesday.
Italian Interior Minister Angelino Alfano said last week that 53 people have left or transited through Italy en route to fight in Iraq or Syria.
One such person was on Tuesday named in Italian media as Maria Giulia Sergio, a 27-year-old woman who has allegedly travelled to Syria to join militant group Isis.