It's advisable to do cardio to keep your cardiovascular system in shape. But, cardio will burn calories which could be used towards building muscle. It's a balance act really. I think you can gain fine while still doing cardio, just don't overdo it.
Mr Khan, ebon00 is right i would still do some cardio but most people work out either for bulking up or cutting down. I dont think you can do both at once cause you get very little results and most people get upset and quit all together