I read a huge part of the Quran (just like I read the bible) and I have to say that I don't see why it couldn't be written by a human being (although I must admit that its much cleaner written than the bible).

Please remark that this is just my opinion and I don't want to offend anyone with it, I have no deeper relation to any religion (although they are all extremely fascinating) and I really don't want to discuss these things because religion is such a subjective topic that its almost impossible to discuss it objectively.