i5 2500k - Temperatures do not match?

Hi!

I just recently finished building a pc for myself for the holidays. Thankfully, all my components were in working order and the Windows 7 installation was a breeze.

I'm planning to overclock the CPU soon, so I downloaded Realtemp to monitor my temperatures. Now here's where I get confused.

In RealTemp, the temperatures on idle are around 27-31C, which surprised me quite a bit. But, in the BIOS, it reports that my temperature is around 34-38C? When I saw this, I immediately thought that these temps were too warm, at least for my taste, for a non-OC'd 2500k on a Hyper 212 EVO cooler.

So basically, RealTemp reports a different (and lower) temperature than the BIOS. I'm confused as to which one is actually true.

What do you guys think?
(Sorry if this is a silly question. I'm new to this stuff   )