I agree with Tony C. Unless you want to buy a new machine, I would leave it unplugged and not use it until a professional has looked it over. It could be something simple now, but if the smell continues and you keep using it, you could fry the whole unit.
Years ago, a mixer I had did a similar thing. It was the motor and when it really started smoking, it was too late. I didn't even try to have it fixed, because I knew the motor would cost more than a new mixer.