In Harper Lee's To Kill a Mockingbird, "prejudice" may make one initially think of white vs. black, but Harper Lee was speaking to any instance when...
...an unfavorable opinion or feeling formed beforehand orwithout knowledge, thought, or reason.
Initially, when Heck Tate brings Tom Robinson to the sight of the alleged rape of Mayella Ewell, he does not mistreat Tom:
...I went down to Robinson's house and brought him back. She identiied him as the one, so I took him in. That's all there was to it.
In a modern context, one might expect nothing else of Tate. He was, after all, a policeman. However, looking back into the history of African Americans trying to find fair treatment in America, some members of law enforcement were not as ethically-driven as Heck Tate. Heck does not beat Tom; he only takes him into custody as the law provides. At the hands of others in many places in the South for hundreds of years, "innocent until proven guilty" was not the standard. As one example, in the Selma to Montgomery Marches in 1965, Alabama state troopers (police) hosed and beat Civil Rights demonstrators on two of the three marches. In the novel, Heck Tate shows Tom consideration as a human being, and we see Heck as a man dedicated to upholding the law, regardless of any other consideration.
Another indication that Heck Tate is not prejudiced takes place in Chapter Fifteen, when Heck Tate and other citizens—men Atticus later refers to as friends—come to the house to talk. (Scout points out:
In Maycomb, grown men stood outside in the front yard for only two reasons: death and politics.)
Jem turns out the living-room lights so they can better see who is there, and they listen to the conversation as it drifts in to them:
"...movin' him to the county jail tomorrow," Mr. Tate was saying, "I don't look for any trouble, but I can't guarantee there won't be any..."
"Don't be foolish, Heck," Atticus said. "This is Maycomb."
"...said I was just uneasy."
Here we can infer that Heck Tate is fearful that something might happen to Tom Robinson. His concern makes it apparent that Heck is not biased—especially in that he is not one of the men in the community that shows up later at the jail looking for Tom Robinson. This group of men are not law-abiding citizens—their fear and/or hatred of blacks has brought them to lynch Tom without benefit of a trial. Heck would have been there to defend Tom, but the others have sent him out on a false report of trouble.
"You know what we want," another man said. "Get aside from the door Mr. Finch."
"You can turn around and go home again, Walter," Atticus said pleasantly.
The other form of prejudice in the story is against Boo Radley. People gossip about him and accuse him of insane and untrue behaviors. At the end, Heck shows his concern for the man rather than that of public opinion when he realizes that Boo killed Bob Ewell to save Scout and Jem:
I've never heard tell that it's against the law for a citizen to do his utmost to prevent a crime from being committed, which is exactly what he did, but maybe you'll say it's my duty to tell the town all about it and not hush it up...All the ladies in Maycomb includin' my wife'd be knocking on his door bringing angel food cakes. To my way of thinkin', Mr. Finch, taking the one man who's done you and this town a great service an' draggin' him with his shy ways into the limlight—to me, that a sin.
Heck Tate is a good man, and shows no prejudice toward Tom Robinson.