Mistake is an action or judgment that is misguided or wrong.Fault places blame or responsibility for a mistake on a specific person or circumstance.

"When I answered the question, I made a mistake." "There is a fault with the Skype connection." "I didn't cause the accident - it wasn't my fault!" Like Jan said, when "fault" is used to describe a personal action, then it is more than a mistake - there is also blame. When talking about machinery,equipment, designs, technology or in fact any process, then a "fault" is something which makes the process not work correctly. In this case, it does not indicate personal blame.