The suspect, named as Djamal Eddine Ouali, 40, was detained under a European arrest warrant in the southern region of Salerno, the reports said.
Ouali was arrested in the southwestern town of Bellizzi as part of a joint operation between anti-terrorist forces and Rome's special operations police, they said.
He was suspected of being part of a criminal network that produced fake documents for illegal immigration, AFP quoted the AGI news agency as saying.
The alleged accomplice of the Brussels attackers would be extradited to Belgium in the coming days, the report added.
Suspicions were raised after local immigration officials checked Ouali's residency permit. Police had been searching for a man with the same name and belonging to the same organization since January 6.
Hundreds of digital photographs were then seized from a counterfeiter's workshop, including three of those who planned the deadly attacks in Paris in November.
One of those photographed was Najim Laachraoui, a suicide bomber at Brussels airport, reports quoted police as saying.
Investigations are ongoing as to how Ouali came to be in Italy and into the networks of which he may have been a part.