The religiously inspired email was sent to three members of Antwerp University staff on Monday. The uni decided not to take any risks and cancelled all lessons for the day.
The daily Gazet van Antwerpen reports that the rhetoric and vocabulary used in the email is identical to the messages contained in a threatening video that appeared on the internet last week.
The paper attributes the film to a group of Syria fighters from Belgium, but public prosecutors have been unable to confirm this.
Federal judicial police have joined the Antwerp public prosecutor's office in investigating the matter to determine whether the email was really sent by Muslim extremists. Antwerp University hopes it can recoup the cost of the evacuation from the perpetrators.