Police special units in the western city of Aachen arrested one man and two women of foreign nationalities in the morning, and two more suspects later in the day, police said.
The suspects "could be connected with the Paris attacks", Aachen police spokesman Werner Schneider told news channel NTV.
He cautioned, however, that "either these indications will be confirmed or they could all go up into thin air". He added that the identities of the first three were yet to be established.
"In this context, there were three arrests this morning. Two women and a man were overwhelmed by special forces and taken into custody. Investigations are currently ongoing."
It added that police had conducted further operations in the area which it could not detail "for tactical reasons", and that "two more people were arrested by special forces in Alsdorf".
European police forces are searching for Salah Abdeslam, 26, who was named by French police as a key suspect in the Paris attacks in which 129 people were killed.
Salah Abdeslam - the younger brother of Brahim Abdeslam, who blew himself up in Friday's attacks - is being sought by French investigators who have issued a photograph of him - describing him as "dangerous" - while Belgium has issued an international arrest warrant.
The French citizen living in Belgium allegedly hired a black Polo, registered in Belgium, which was found near the Bataclan concert venue in Paris, where three attackers killed 89 people.
Salah Abdeslam was in Austria in September, telling police after arriving from Germany with two men that he was "on holiday", Austrian authorities said today.