Consciousness in Nibbana
There are two types of nirvana: saupādisesa-nibbāna (nirvana with remainder) and anupādisesa-nibbāna (nirvana without remainder) (Iti. 44). 

It is true that for one who has attained anupādisesa-nibbāna there will be no more consciousness. This is because someone who has attained anupādisesa-nibbāna is dead*. It is the equivalent to the more familiar parinibbāna - "complete" nirvāna. For one who has attained saupādisesa-nibbāna, there is still the physical and mental formations that have been created as a result of being born as a human that need to work themselves out, including consciousness.

* Conventionally speaking; technically, they have become free from death, since they have become free from birth (arising).