Are you sure your pointer is really pointing to an actor? How have you set the pointer to point to the actor? If this script is being used on a Blueprint class, you probably aren’t able to point to an actor unless it’s being used inside a scene and the pointer is being altered inside the scene.
If you’re trying to set the pointer using BP nodes, you should set it to BlueprintReadWrite.
If you’re straightly using the class, then I’m guessing that the class is inheriting from AActor as you said it’s an actor, remember to assign the actor through engine’s internal scene combo-box.
If it’s something else, maybe share the error as well and we’ll find it out but I’m mostly sure that your pointer is nullptr.