Of course, briefly, you can do cardio at the same time as building muscle but you have to go about it in the correct way. You need to find out how to do cardio well consequently it does burn fat but is not to the loss of the lean muscle that you've gained.
The most successful way to do cardio while building muscle is by choosing an exercise which moves your body around more than any other kind. You can lose calories by walking but jogging and running are far better. It's the intensity of the cardio that counts; short and sharp will enable the increase in muscle.
Too much aerobic exercise may give you stamina for distance and it will use up fat, but it won't build muscle if the body doesn't get enough rest.
To do cardio while building muscle, you need to do really intense cardio for something like fifteen to twenty minutes three or four times a week. The intense exercise should be for the whole of the period without rest. You won't lose more weight or build more muscle if you carry on for longer than twenty minutes and neither will you do so if you do it every day. The intensity of the cardio will burn the calories and body fat but you need that rest in between.
Now you need to choose which sort of cardio you can maintain at high speed for fifteen to twenty minutes. The following are good ways:
Running or jogging
Treading water in a pool (hard)
However, you need to remember that you will be moving your body so much that you can't read a book while you do this exercise. Choose whichever method suits you best and which you can maintain a high intensity with.
On the days when you're not doing cardio, you can do separate muscle building resistance exercises with weights or weight machines. The cardio will then help with recovery from the weight training and you'll burn a few more calories.
If you want to build a lot of muscle, cardio can help because it obviously improves the condition of your cardiovascular system but it will burn the excess calories you will need to eat to build muscle effectively. If you do the eating without the cardio, some of those calories will turn to fat.
Doing cardio at the same time as building muscle is completely promising but do seek advice from a professional for the right exercises and timings, mainly if you don't generelly.