I was taking apart an old mouse and I noticed something that looked suspiciously like a microprocessor. It looks like the processor on my UNO, just with 16 pins instead of 28. It has the motorola logo on it and it looks like the part number is 331021-2001. Could anyone tell me what kind of microprocessor this is, if it is one at all?
There are MANY chips that are made in the same shape as the ATmega processor and very few of them are microprocessors. The Motorola chip in your mouse is likely to be a custom mouse chip.
Okay, thanks.
The Motorola chip in your mouse is likely to be a custom mouse chip.
Which is to say, a pre-programmed microprocessor/microcontroller whose function can't be changed. 
With so many of the new microcontrollers being flash based, I'm a little surprised that there isn't more "hacking" activity discovering re-programmable micros in consumer products...
IMO it's worth grabbing the part number off it and googling "whatever2858120 datasheet" to see what comes up.
You never know!