Some 3,000 Tunisians have joined the ranks of jihadist groups fighting in neighbouring Libya, as well as in Syria and Iraq, according to officials. The United Nations puts the figure at 5,000.
With the Islamic State group losing its main Libyan stronghold of Sirte and the jihadists under pressure in Syria and Iraq, concern has been growing in Tunisia that many will return to the country.
Protesters at Sunday's rally -- many wrapped in Tunisians flags -- shouted "No to returning terrorists!" and "All Tunisians against terrorism!"
"Tunisians need to be reassured by a real political will that makes it clear these criminals won't be allowed to return," said one of the protesters, 33-year-old civil servant Shahnez Mili.
Tunisian authorities have arrested several dozen alleged jihadists in a growing crackdown on extremists in recent weeks.
Authorities stepped up their efforts after Tunisian Anis Amri was identified as the primary suspect in last month's attack on a Berlin Christmas market that killed 12 people.