Switzerland is on high alert after Islamist militants killed 130 people in Paris in November. A week ago, two Syrians were arrested near the French border on suspicion of having links to Islamic State. Traces of explosives were found in their car.
The attorney general's office did not name the accused, but the Islamic Central Council, which says it is the largest Muslim organisation in Switzerland, identified him as the German head of its multimedia department, Naim Cherni. He was either 23 or 24 years old, the spokeswoman said.
According to State Attorney Michael Lauber, the accused traveled to Syria in October and interviewed the leader of a jihadist umbrella group as well as the leader of Jabhat al-Nusra, which is affiliated with al Qaeda.
He subsequently released a roughly 40-minute video, in Arabic with German subtitles, documenting their exchange.
Lauber said he "presented his journey to embattled regions of Syria in a video for propaganda purposes, without having explicitly distanced himself from al Qaeda activities in Syria."
The Islamic Central Council says on its website it seeks to promote the recognition of Islam in Switzerland and that it had more than 2,500 members at the end of 2012.
A spokesman for the council said earlier on Saturday that its leaders were unable to make a statement immediately but would respond at the press conference with Cherni on Monday morning in Berne.
The Swiss government on Friday announced it had added 86 employees to what it called its "terror fighting" activities within the federal police, intelligence service and border patrol agencies.
Lauber recently opened a criminal inquiry on the basis of a "terrorist threat in Geneva" against unknown persons suspected of belonging to a criminal organisation and of violating the ban on al Qaeda or Islamic State.