The man identified only as Shaas EM allegedly joined the Islamist group in 2013 and stayed with them until at least August last year, having "taken part in various military operations" and delivered food supplies for the IS, they said in a statement.
Prosecutors declined to tell AFP when and how the suspect entered Germany, which last year took in over one million asylum seekers, around 40 percent of them from war-torn Syria.
They said there was currently "no evidence of concrete attack plans" and no known links between the suspect and the recent bloody jihadist attacks in France and Belgium.