"The discovery is significant and quite important for us because of the quality of the marble and the excellent workmanship of the sculpture," said Paolo Caputo, a local heritage official.
The statue is of a woman and was discovered in October just off the shore near the town of Baia in what is already an underwater archaeological park.
The figure is headless and without arms.
"We do not yet know whether it is a divinity or a member of the imperial family," Caputo said.
The area around Baia was a thermal resort that was popular in Roman times and has several villas.
One of them was confiscated by the Emperor Nero (37-68 AD) and turned into a summer residence and it was there that the statue was found.