Police spokesman and Superintendent Ajith Rohana said the family members were arrested yesterday off the coast of Talaimannar in the north as they were returning via sea.
They had fled to India in 2004 from Mannar and spent time in Rameshwaram. Navy intercepted their boat yesterday.
The family members included three youths aged 21, 19 and 15 years and their parents aged 44 and 38, Rohana said.
The motive of their fleeing Sri Lanka would be investigated, he said.
There was a large influx from Sri Lanka's north and east to Rameshwaram by boats during the decisive military clashes between the LTTE and the Army five years ago.