Prejudice doesn't just fall out of the sky and into your brain. So where does it come from?
Well... prejudice starts usually from stereotypes, which are usually just made up and not true about the specific group. Prejudice can start from the people around you. People usually just go along with what their family and friends think. Prejudice also starts from personal experiences. For example if someone of a specific race does something wrong to you, you might think that the whole race is like that.
Prejudice still exists today. People say it is even worse today than it was in the past. They say that it is worst due to mass media.
Prejudice can be avoided though. Read this article to find out how. http://ctb.ku.edu/en/tablecontents/sub_section_main_1173.aspx