Yes, to do this please:
Log in and go to Play > Multiplayer > Arena.
Select the Maths or Pastoral class you would like to spectate (the drop-down below where you select the Arena game mode).
Click the 'spectate mode' button on the game you would like to spectate.
You're ready to go!
If you would like to play in the game and not spectate please click on the larger rectangle.