Contrary to what Bliss said, one accumulates karma for all activities, including thoughts and intentions.
Karma does not come in good and bad varieties though. It's more like a record of the kind of person you are. If you act dog-like you'll acquire dog-like karma, which will in turn make you even more prone to acting dog-like and, ultimately, you'll be reincarnated as a dog.
The idea that there is good or bad karma or that it gives out reward and punishment is a product of Western thought grossly misunderstanding this Eastern concept.