A homemade explosive device went off shortly after 10.15 p.m. on Sunday outside a branch of a courier service in Pangrati, central Athens.
The blast on Astydamantos Street is believed to have been caused by a gas canister.
Police and fire-fighters arrived within minutes of the blast.
No injuries were reported, though the building in which the ground-floor courier office is housed suffered minor damage.
Police were investigating the incident.