It looks like some kind of stud fastener, made of creamy grey plastic, but it doesn't ring any bells. Don't think it comes from a PC, keyboard, etc., could be something like an old-style floppy disk box but I haven't had one like that in years. The head of it is about a centimetre across, and it's about a centimetre long.
It's probably completely unimportant, but not knowing is beginning to bug me.
Does the look of it ring any bells with anyone?