First, what software are you using? I recomend Motherboard Monitor.
In my case, BIOS and software temps are the same. But for sure your mobo maker know where to read the temps, so believe BIOS temps!
Another issue is that the termal probe can be miscalibrated, giving some over or under values. What are your temps at full load? Can you also give mobo, CPU, and all details of your computer/enviroment?
DIY: read, buy, test, learn, reward yourself!