A part can be overheating even if you don't feel it. Also, it could be that there is a virus or malware on the tablet causing this as well.
First try turning on the tablet in "Safe Mode" and see if the message shows up while in there. You can't do a lot of things in that mode, but if the message never shows, and it never turns off, then you know it is something on the device causing it then you need to find and remove.
However, if it does it in "Safe Mode" as well, then I would have it looked at for hardware problems.
To get into "Safe Mode" please do the following.
1. First turn off the tablet.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.