Is Sidious afraid of Obi-Wan?
Grevious was a mere distraction to get Obi-Wan off Corascant. During this time, Sidious unveiled his last act to turn Anakin to the darkside. Why send Obi-Wan away though? Yes, Anakin and Kenobi were best friends, but Anakin was already walking the path to evilness. Was Sidious afraid that Obi-Wan could save Anakin?
At the beginning of the movie, Sidious says, "No, leave him". Yes, Sidious definately wanted to get rid of Obi-Wan.