A group of former ISIS militants, women and children, some of them orphaned, returned to Bosnia on Thursday, the prosecutor's office said.
Hundreds of people are believed to have left Europe to fight for ISIS in Syria and Iraq, and many are now in detention camps waiting to be handed over to their countries of origin.
"The suspects ... are under investigation for the criminal offences of organizing a terrorist group, unlawful formation and joining of foreign paramilitary or paramilitary formations and terrorism," Reuters quoted the office as saying in a statement.
"Some of these persons were sought on international arrest warrant by order of the Court of Bosnia and Herzegovina," the office said without saying how many people have arrived.
Bosnia's presidency chairman said early in December that 24 people were expected to return to Bosnia.
Authorities said they had carried out security checks on all returnees.
Bosnia has been preparing to take back and put on trial nine of its nationals suspected of fighting for ISIS in Syria since October but their repatriation has been postponed twice after Turkey carried out a military operation into northeastern Syria to fight Kurds.
Under Bosnia's criminal code, citizens who leave to fight in foreign wars must be prosecuted under terrorism charges.
Bosnia's state court has tried and convicted 46 people who returned from Syria or Iraq over the past few years.