There are a few select able races which you can choose to play. Every one will start off as a Terran, but by completing missions you can choose other different types of alien race to play.
 
Alien races in the game:-
Terran Race
Aspha Miner
Marauder
Dark Marauders
Berserkers
Viral 106 Race
The Collective Race
Guardian
Kal-Zul