My Athlon II X2 does the same thing. Core should be more accurate, however it appears mine (and yours) may be miscalibrated/misdetected. A good way to check is to see if at idle (or even unOC'ed) core temp goes below ambient. If it does, the core temp is wrong as that is physically impossible.
Thanks for the reply. My temperature is actually exactly the ambient temperature. I also noticed after both are under load, they both go up the same # of degrees. Anyway, I guess I will listen to core temp.