Could be the drive, the media, or a lack of system resources.
You could try burning at a lower speed, or using better quality media. Also, I like to leave the computer alone when burning discs so as to free up CPU cycles for burning. Also, I shut off the screen saver (use a hot corner) so that doesn't kick in during a burn. Lastly, I make sure I don't jostle the computer (I have a laptop but a desktop can be jostled just as easily).
Apple has had some problems with superdrives recently. I had to have mine replaced. If you have a newer computer that could be the case. If you're under warranty the repair can be done at a retail store in 20 minutes.
Well I'll be doing some testing like... burning a CD while the computer is connected to the AC. Try other things to and see how the computer is working.
I have a new macbook pro so if this keeps happening I'll take it to warranty.