if you don't do anything but sit around and play on the computer and are not gaining weight, then it means you (intentionally or not) do a good job of eating only the amount you need. if you ate more than you need, then you'd gain weight, and less then you'd lose.
the running should slowly start to show if you don't start eating more to compensate for what your burning during exercise (it's quite likely you may start eating more without even realizing it... the body hates to lose weight).
congratulations on starting to exercise, keep it up!
