gigabyte GA-78lmt-s2 motherboard

Solution
If the temp is 40C then don't worry about it. If the temp is going up to 60-65C you need to do something like buy the aftermarket cpu cooler or open the side panel of the case to cool down.
It is little bit hot, some of CPU has max temp is 65C and other is 70C, because you don't post what CPU you have. But you can check it by yourself, for example, FX-6100 is 70C, like here: http://www.cpu-world.com/CPUs/Bulldozer/AMD-FX-Series%20FX-6100.html, go to the "Electrical / Thermal parameters", you can see "Maximum operating temperature= 70°C".

You can add the aftermarket cpu cooler to cool it down.