Police investigators in Thuringia, Hamburg, North Rhine-Westphalia, Saxony and Bavaria carried out the raids.
The raids carried out due to a suspicion that suspects were planning a serious act of violence against the state, but investigators say there was no concrete evidence of an imminent attack.
Germany has so far been spared large-scale jihadist attacks.
But Europe's biggest economic power has been shaken by two assaults claimed by the Isis and carried out by asylum seekers – an axe rampage on a train in Würzburg that injured five, and a suicide bombing in Ansbach in which 15 people were hurt.
Police said this month they had foiled an alleged plot by a Syrian refugee to bomb one of Berlin's airports.
The cases have fuelled anxiety over Germany's record influx of nearly 900,000 asylum seekers in 2015.