Is it ok for a Muslim to be a godparent? What does it say regarding this?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

If you mean the common definition of "godparent" which is the person who attends baptism of a baby, assists in his cultivation as a Christian and looks after him to assure that he implements his religious duties, this is forbidden for a Muslim to do. By doing so he will supervise disbelief, witness it, follow it and guide to it; we seek Allaah's refuge from that. In fact, this is an act of apostasy from Islam if it is done by a Muslim. We have stated in previous Fatwa: 90151 that merely attending baptism is not allowed, then how could it be allowed to supervise or follow up the matter and raise the child to be a Christian. No doubt, it is an act of totally confirming the disbelief and even calling towards disbelief and guiding to it.

For details read Fatwa: 88293 about the relations with non-Muslims and Fatwa: 83972 about converting People of Book to Islam.

Allaah Knows best.