I recently put a scope on a 9mm pistol, but decided the scope was useless. Is there any way to take it off the gun? I would just find another pistol, but the pistol I have is currently in top condition.
According to The New Vegas Wiki:
Once a weapon mod is attached to a weapon it can not be removed and remains a permanent feature of that weapon, along with its added attribute. However, this could not always be a good thing. For example while an extended magazine is almost always beneficial, a scope on the other hand has pros and cons. It may increase maximum range, but makes it harder to use in close combat situations.
Sorry, it appears you're out of luck.
Actually, if you are playing on PC you can download The Weapon Mod Menu which allows you to take off weapon mods. If you're not on PC then you'll just have to find a normal 9mm Pistol.