“Seventeen people have been arrested since the beginning of November in several security operations,” the source told AFP.
Those held, whose identities were not revealed, were preparing attacks on hotels or buildings used by the security forces, the source added.
Without elaborating, the source said several of them had spent time abroad with members of jihadist organisations such as the Islamic State group.
The news comes after the interior ministry said Monday seven women have been arrested for posting propaganda on the Internet on behalf of the Tunisian affiliate of IS, Jund al-Khilafa.
It also follows an anti-terrorist sweep Sunday on Mount Mghilla in the centre of the country after the gruesome beheading there by jihadists of a 16-year-old shepherd.
One soldier and a presumed jihadist were killed during that operation, the defence ministry said. No group has yet claimed responsibility for the shepherd’s murder.
Thousands of young Tunisians have travelled to Iraq, Syria and Libya to fight alongside Islamic extremists, according to the authorities in the North African country.
At home, IS has said it was behind two attacks targeting foreigners – at the National Bardo Museum in March, killing 21 tourists and a policeman, and at a hotel in Sousse in June, killing 38 tourists.
Dozens of members of the security forces have also been killed by extremists since the 2011 revolution that sparked the Arab Spring.
The Tunisian authorities say they have been particularly affected by the chaos in neighbouring Libya, where IS has established a presence.
Tunisia has begun building a border wall some 200 kilometres (125 miles) long, with the aim of stemming the flow of contraband weapons across the frontier.