No, 120 isn't a default ID or whatever. If 120 is reported, an object with this ID has been selected, unless the method is faulty which i'm not aware of.
However, it may be related to the fact that you call the picking all the time, not just when a mouse button has been pressed. I assume that your mouse-click-method sets mouseX and mouseY? If so, let it set a flag like "clicked=true" too and do the picking only if this flag is set (and reset it afterwards). See if this fixes your problem.
The picking doesn't care if a mouse button has been pressed or not. It just fires a ray into the scene according to the coordinates you give it. If you do this every frame, so be it...
If the "120"-problem remains, please try to find out which object's ID this is and where it is located.