Racism is not the same as prejudice, bigotry or ignorance. Black people, for example, cannot be racist but they can be prejudiced. They can be prejudiced against white people for example. They cannot, however, be racist because racism describes various aspects of a system of disadvantage based on race. Black people cannot be racist because they do not benefit from such a system since such a system was designed specifically to deny them equality in American society. 
I am white, of European descent, but am somewhat prejudiced against white people because they are frequently racist and rarely genuinely acknowledge the the racist reality faced by non-whites in American society.