Yes. It is. Any drug has the chances of making the user addicted.
You can consider caffeine, alcohol, tobacco, and yes even television all as a drug, because it can make the user addicted.
Ritalin controls the endorphins in the brain to "fire" at certain times to "relax and calm" the patient. So what happens when you stop taking it? The result is a lack of a certain endorphin in your brain causing you to "crave" that feeling produced from Ritalin.