Fallen Gaurdian nailed the first script but if your NPC was doing another action I wouldn't use the second script might I suggest just taking the belt away from the NPC?
void main ()
object oNPC = GetObjectByTag("my_npc");
object oArmor = GetItemInSlot(INVENTORY_SLOT_BELT,oNPC);
AssignCommand(oNPC, ActionUnequipItem(oArmor, TRUE));