Police in the western city of Duesseldorf say the 50-year-old man, who wasn't named, was arrested in the nearby town of Ratingen.
In a statement, they said further details would be announced at a news conference Wednesday afternoon.
Following the explosion at the Duesseldorf-Wehrhahn train station in July 2000 suspicion quickly fell on far-right extremists, because those hurt were recent immigrants from the former Soviet Union.
The victims were on their way home from a German-language class at the time.