The raid came just days after police carried out a string of coordinated raids in Berlin and North Rhine-Westphalia, DW wrote.
Police searched the apartments of two men suspected of having ties to a terrorist organization in Syria. One of the men, identified only as Bassam, was said to be a 32-year-old refugee from Syria.
According to German news magazine "Der Spiegel," Bassam is suspected of having been a commander in the "Islamic State" (IS) terrorist organization. The magazine reported that he had once been trained as a suicide bomber.
A spokesman for the Federal Prosecutor's Office said no solid plans for an imminent attack were found during the raids.
The raids were the second set conducted this week, after police launched an investigation into three Algerians with suspected links to IS.
Following the earlier raid, police said they had been tipped off by a photo showing one of the men training as a terrorist fighter in Syria.
It wasn't yet clear who the second suspect in the Mainz raid was or how the people living in the searched apartments may have been connected.
