Yes. A fire extinguisher (of at least 1kg) must be present during inspection. The expiration date is also checked, so make sure that your fire extinguisher isn't expired. You can always find a year written on the fire extinguisher.
In addition to a fire extinguisher, cars in Belgium must also have a warning triangle, first aid kit and safety vest.
On the following link you will find more details about the inspection of the car.