It could be any number of things.
Are the temps under load or at idle? Where are you getting these temp readings from (From BIOS or another program)?
Are you getting a BSOD? Is your computer shutting down because of these temps?
Make sure that you are reading the APU/CPU INTERNAL temp with a temp program that provides accurate temps in to 60C-70C range. The max Internal temp, sometimes referred to as "core temp" or similar is 71C for your processor. AIDA64, Core Temp, OCCT and HWiNFO are applets known to report the Internal APU/CPU temp correctly in the 60C-70C range. If you are reading "CPU Temp" then you are NOT reading the Internal APU/CPU temp. The "CPU temp" is the reading for the CPU socket, not the Internal APU/CPU temp. The CPU socket typically runs 10C-25C higher than the APU/CPU Internal temp.
The OEM AMD supplied fan will properly cool the APU/CPU it is supplied for if all is running properly and the PC case has proper airflow thru it. The first thing to check is to see if your CPU/APU and case fans are all running at 100% speed. You may need to adjust their speed in the BIOS or O/S so they can run at full speed as needed instead of at partial speed. The APU/CPU fan speed will vary with APU/CPU Internal temp and load. The APU/CPU frequency and vcore vary constantly to provide the best performance based on Internal APU/CPU temp. If your APU/CPU reaches an unacceptable Internal temp, the frequency and vcore will drop to allow the APU/CPU to cool properly.