The light sould falsh when it's parked. It means the system is active and the car should not start with it flashing. When you put the encoded key in the ignition and turn it, it signals the computer that it's the correct key for the car and that its ok to start and the computer lets the car start.
As for the light coming one while driving...well that's sounds like a diagnostic service needs to be done to find out what's up with that.