I am on a no-carb diet and lost 12lbs in 24 days. But my biceps have retains the same mass. Is this healthy?

Normal. You do not want to be losing muscle when losing weight. Also, you cannot lose weight from specific areas, fat is burned from wherever. Be careful with no carb diets. Your brain needs carbs to work properly. If you don't have carbs your brain uses ketone bodies made from fat, which it does not like as much. A balanced diet & exercise is the best way to lose weight & keep it off.
No-Carb No-Good. For the trillionith time, just kidding-but close, a no-carb diet wil not work in the short or long term. As soon as you start eating carbs-- you will gain some weight back--the next day, and you will feel sad and defeated, again. The fact that your body hasn't been digesting your biceps muscle is just because it just hasn't gotten around to it yet. No this not a healthy eating plan to lose weight.