A decision is to be made over the course of the day on whether to remand them in custody.
Searches were conducted in several states; the suspects were detained in the cities of Ulm, Delmenhorst, and Munich, a statement from the prosecutor said.
Money is alleged to have been collected for Hayat Tahrir al-Sham (HTS), formerly the official Syrian branch of al-Qaeda, which today controls much of the country’s remaining rebel-held territory.
The German prosecutor said an HTS member based in Syria had played a central role within the terrorist-financing network.
The man allegedly called online for donations that were to be spent on buying weapons and supporting fighters.
The funding network is thought to span across Europe.