Here's why:

* Normal force is a reaction force. It's the force a surface exerts on an object in response to the object's contact with the surface. It acts perpendicular to the surface.

* Frictionless doesn't mean weightless. An object on a frictionless surface still has weight (due to gravity), which is a force acting perpendicular to the surface.

* Newton's Third Law: For every action, there is an equal and opposite reaction. Since the object exerts a force on the surface due to its weight, the surface exerts an equal and opposite force on the object, which is the normal force.

In summary: A frictionless surface doesn't affect the normal force. It simply means there's no force opposing the object's motion *parallel* to the surface.