Just like any other activity- if you move and get your heart rate up for long enough then it could count as a work out.
"For any activity to count as true exercise, it has to meet certain parameters, like lasting at least 10 continuous minutes (so those stairs you took or that walk from your car to the store doesn't count as a workout), it has to elevate your heart rate to an aerobic level (that "hard" feeling I mentioned above), and more. " from
www.sparkpeople.com/resource/fitness_artic
les.asp?id=1209