It would depend on what it is connected to when you are seeing this. While connected to the USB port of a computer, many cannot provide the necessary power to charge the device, but it does supply some, and the iPad will charge a little bit. However, when it is connected to the power adapter that comes with the iPad and plugged into the wall, you should see it charging just fine.
IPad says not charging
3 replies
Why does my I pad say "not charging" and still charges