They mean basically the same thing, but with a slightly different flavor. If somebody asks "How are you?", if you answer "I am fine" or "I am okay", it would mean that you are doing well. If you said "I am all right," it is often taken to mean that you are doing basically all right, but things could be better. Also, if someone was asking whether you were hurt for some reason, you would be more likely to answer "I'm all right." and perhaps, "I'm OK." Also the meaning would change with the tone of you voice. If you say "I'm OK" in a 'flat' voice, with no emotion, it can be taken too mean that thing aren't as good as they might be.

definitely same~

I think they are all the same too