At the end of Death Note, after Light is revealed as being Kira, Mikami goes on a little rant after their plan failed thanks to Near having switched the real Death Note. After that, however, Light denies knowing anything about Mikami.
After Light is shot several times by Matsuda Mikami then stabs himself with his pen, the fountain of blood and yelling grabs everyone's attention and as everyone goes to try to treat him, Light escapes.
However when Light denied knowing Mikami, Mikami looked depressed as if he had just been betrayed by his "god", but his suicide gives Light a distraction to flee.
So before Mikami committed suicide, was he still having faith in Kira?