Yes, it should be the second highest. Your cell radio isn't just the mobile data. Your phone and cell towers are always communicating, requesting and receiving information from each other (these are referred to as handshakes and that's how you can triangulate where someone's phone is...the constant communication). So as long as you're not in airplane mode, your cellular service is active and using battery. And since it is constantly on (even when the screen is off) it is the second highest battery drain.
One would think the OS would use more battery, but Kit Kat is pretty battery efficient so that leaves cellular transmission as the second highest. It also increases with the amount of text messages you send since there is a communication between your phone and cell tower when that occurs.
Turbo-Shot from my Ballistic Turbo