|A Swiss border guard controls the area at the Bardonnex border|
Prosecutors said the German suspect is a board member of the Islamic Central Council of Switzerland (ICCS).
He is suspected of using videos of his trips to Syria for propaganda purposes.
Switzerland remains on high alert following the terrorist attacks in Paris on 13 November that left 130 people dead.
Last week, the city of Geneva raised its security alert following a warning that a cell of so-called Islamic State (IS) was in the area.
Swiss prosecutors did not name the suspect, but the ICCS said - in a statement announcing a press conference for Monday morning in Berne - that Naim Cherni would be among those taking part, and would give his personal response to the allegations.
A statement from the Swiss attorney general's office said that criminal proceedings had been opened against the ICCS board member on suspicion of violating laws banning extremist groups such as al-Qaeda and IS.
The suspect is said to have produced videos of his trips to conflict zones in Syria for propaganda purposes.
The attorney general's office said the man was "accused of having interviewed a senior member of the jihad umbrella organisation Jaish al-Fatah, of which the Syrian al-Qaeda branch, Jabhat al-Nusra, (al-Nusra Front) is also a member".
It said he had made the video "without explicitly distancing himself from al-Qaeda activities in Syria".
The office indicated that the man had not been arrested.
Separately, a statement by the authorities also confirmed that charges had been filed against four Iraqi citizens, accused of preparing a terrorist attack.
In total, Swiss authorities say they are conducting 46 criminal cases related to "jihad motivated" terrorism.
Last week, President Simonetta Sommaruga said a "foreign authority" had warned of a possible IS cell in Geneva. Security was stepped up.
In a separate development, two Syrians were arrested on 12 December near the French border, with police saying that traces of explosives were found in their car.
IS said it carried out the attacks in Paris on 13 November. Two men linked to the attacks - Salah Abdeslam and Mohammed Abrini - are still on the run and investigations have been launched in several European countries.