OK MBM gets it's information from the same place as what the Bios does, what you need to make sure is that MBM is reading the correct sensors for your motherboard, I don't know what your motherboard is but if you navigate to the "Motherboard List" section and choose your maker and model it will give you the listings of what sensors report back what temps.
If you had the correct ones you might need to tweak your settings as the BIOS might be correct or out ask in the forums here in the correct section for your MoBo if the onboard heat sensors are correct or out, if so you can tweak MBM and calibrate the settings of the readouts so they are correct.