Police sealed off a Brussels square and called in bomb experts after a man was seen wearing a thick coat on a hot summer's day with wires protruding from underneath, but he turned out to be a student who said he was researching radiation levels.
"The way in which he reacted initially was not normal, which is why we had to use such measures," a police spokesman in the Belgian capital told reporters after Wednesday's incident.
He said the bomb squad had used a robot to carry out an initial check which revealed metal plates underneath the man's coat, further raising suspicions. The man was taken in for questioning.
Brussels airport was the site of an Islamist militant attack that killed 32 people in March. Authorities are on high alert before a national holiday on Thursday, which police fear could be a target after last week's attack on crowds celebrating Bastille Day in the French resort of Nice.