Yes and no, some may find that the comments are racist, some may find that they funny, and some may feel a little of both. Shows like the Big Bang Theory and even the Family Guy make fun of various things and race is one of those that are on the list. In the end it is all about perception of the audience.
No, the Big Bang Theory characters are not being racist, because they are simply making fun of their friends. It is important to a friendship that a person can joke with another about the way that the person is. This is all the Big Bang Theory characters are doing. If they continued to do it, after the person said they didn't like it, that would by racist and bullying.
While race is a questionable attribute in humans, the Big Bang show writers have set this question in motion. Although Raj Koothrappali may be somewhat dark skinned, he would probably be considered to be the same "race" as Leonard Hofstadter, Sheldon Cooper, and Howard Wolowitz. Most cultural anthropologists consider Indians to be Caucasian.