Lt.-Col. Yury Bezler was told on Monday he has two weeks to leave Canada. The Russian Embassy's website describes Bezler as an assistant military attaché in Ottawa. He is one of three defence attachés working at the embassy.
It isn't clear why he is being expelled.
A spokesperson for Foreign Affairs said in an email Monday evening, "We do not comment on the status of diplomatic personnel."
Earlier Monday, Foreign Affairs Minister John Baird issued a statement condemning Russia's "provocative actions in Crimea and elsewhere" in Ukraine. "If this pattern persists," Baird continued, "Russia will continue to face increased isolation from the international community and suffer further serious consequences as a result of its action."
The comments from Baird came after unrest flared once again in Ukraine. Pro-Russian demonstrators seized parts of the eastern Ukrainian cities of Kharkiv, Donetsk and Luhanskon Sunday. The protests have ignited concerns Russia will now try to annex those cities as it did with the Crimean peninsula.
Sources tell CBC News no other Russian diplomats have been declared persona non grata at this time.
In early March, Ottawa ordered nine Russians soldiers participating in military exercises in Canada to leave the country.
A week later, Russian diplomat Andrey Gorobets was stabbed in altercation at an apartment building in Ottawa. Gorobets left the country shortly afterward and a Canadian Forces reservist has been charged with aggravated assault.