A police statement says the parcel arrived at the police station in Itea, nearly 180 kilometers west of Athens, today and immediately raised suspicions.
Bomb disposal experts destroyed it in a controlled explosion.
The anti-terrorism squad is handling the investigation, and has made a public appeal for information on the incident. Militant anarchist groups have carried out parcel bomb attacks in the past in Greece, including a spate of attacks in 2010 blamed on the Greek group Conspiracy Nuclei of Fire.