Bomb disposal experts were called in on Thursday to examine a package that was intercepted by security at the ruling SYRIZA party's headquarters.
The package was intercepted after being put through an X-ray machine at the party's downtown Athens offices on Koumoundourou Square.
Earlier in the day, a makeshift explosive device went off outside a church in the central neighborhood of Kolonaki, injuring a police officer and the church's caretaker.
That blast comes less than a month after a powerful bomb was detonated outside the offices of Skai television and Kathimerini newspaper, causing extensive damage to the building's facade.
No one has claimed responsibility for the two attacks and there are no indications that the incidents are related.