  The magnetorotational instability(MRI) in the Kerr spacetime is studied on a
3+1 viewpoint. The Maxwell's equations are expressed in a circularly orbiting
observer's frame that co-rotates with matter in Keplerian orbits. There exist
large proper growth rates in MRI around a rapidly rotating black hole. The
large "centrifugal force" and the rapid variations of magnetic fields are
caused by the rotation of spacetime geometry. As the result, in the extreme
Kerr case the maximum proper growth rate at $r=r_{ms}$ becomes about twelve
times as large as that in Schwartzshield case.
