According to The Associated Press, Belgium's federal prosecutor's Office said the investigation was launched after Nato's security services alerted Belgian military intelligence to potential espionage concerns.
Authorities said they searched the suspect's home and workplace inside Nato's military headquarters on Thursday before arresting her on Friday.
The prosecutors said the woman, identified only as “a Canadian citizen of Chinese origin”, is under investigation for alleged links to a foreign state.
“She is suspected of spying on behalf of a third country and of being a member of a criminal organisation,” the federal prosecutor's office said in a statement.
The investigation centres on the Supreme Headquarters Allied Powers Europe (Shape), Nato's operational military headquarters in Mons, Belgium, where military officials oversee joint planning, strategy and operational command for the alliance.
The alliance's political headquarters remains in Brussels, where ambassadors from the 32 member states regularly meet to discuss defence policy, cyber threats, military spending and regional security. Nato's cyber security centre is also based at Shape.
