Basically yes - be sure it's a logic-level MOSFET (that can be switched with 5V logic - most require 10V). The 5V fan might run a bit fast on 9V - so you are adding a resistor to drop the voltage a bit? You would normally do that on the high side, and switch with a n-channel MOSFET or NPN transistor on the low side.
Is the fan a brushless motor BTW?