state of mind
People all over the world of numerous faiths practice aikido. The main hangup with some Christians seems to be the bowing, specifically to the photo of the Founder of aikido. While some people like to make this into a religious gesture, most do not. Bowing is just a way of showing love and respect for the man that made this wonderful art available to us.
In my mind, aikido is the most "Christian" of all of the martial arts. I sincerely hope that you have a great experience!