Could be the starter relay...mine went bad after a ride in a heavy rainstorm. Without pressing the start button, with the key (power) on, the starter would spontaneously start. Bike started up on its own and kept engaging the starter even after it was running. (I was able to ride by starting the bike and then pulling the relay.)
It's an inexpensive part, may be worth trying a replacement.
Relay...$11.53 on Bike bandit
[ This message was edited by: Tabletop on 2007-03-19 18:10 ]