An unfair bias is a sentiment that a person has for something which influences his decision about that thing. This leads to prejudice because a person prefers one person or thing to another.
When a bias is considered unfair, it means that the person who has the bias is unwilling to let logical thinking and facts to make decisions.
Please note that your question is incomplete and as a result, i am giving you a general overview to help you get to the correct answer.
Some examples of unfair bias includes:
A manager hiring more Asians because he thinks they are better.
A football fan booing a black player because he feels he is inferior, etc
