Ipod Temperature.

I have an Ipod touch 4th Generation running IOS 4.3. My Ipod will randomly show an alert saying "Your Ipod needs to cool down before you can use it". When it says this, the iPod does not feel to hot or too cold. I have restored the iPod before, but the problem still remains.

Does anybody know what this is or how to fix it?
Thank you for your help!