The most obvious example of prejudice in To Kill a Mockingbird is the behavior of the Ewells. Mr. Ewell, the father of Mayella Ewell, who has accused Tom Robinson of rape, is blatantly racist. When he finds out that Atticus is going to try to the case, he expresses disbelief that anyone would the word of a black man over a white man.
Prejudice is also seen in the behavior of the mob that attempts to lynch Tom at the jail. They are presuming Tom’s guilt and do not want to wait for a trial. Even children get into it. At school, Scout is taunted by her classmates because her father is defending a black man. At one point, even a cousin teases her about it.
The jury itself can be supposed to be prejudiced, since they find Tom guilty without any real evidence. The only explanation seems to be that they are not going to let a black man off the hook if he is being accused by a white person.