Losing weight requires that you reduce your intake of calories and increase the amount of exercise you do. Usually, the exercise used to burn the most calories is a cardiovascular workout. Combining high intensity aerobics with a calorie restricted diet will lead to some muscle loss. There are however, ways you can decrease the amount of muscle lost when losing weight.
First, keep doing your strength training routine. By lifting weights, you're still burning calories (like cardio) but at the same time stimulating your muscles just as you would if you weren't trying to lose weight. While you won't have all the calories you need to grow your muscles, a good strength training routine will allow you to keep more muscle when compared to stopping it all together to fit more cardio into your routine.
You should also try losing weight slowly by cutting fewer calories from your diet. When you remove a large amount of calories from your daily intake, your body becomes starved and will begin breaking down muscle tissue for extra energy. By cutting calories at a moderate moderate amount, your body will be able to avoid breaking down muscle by looking elsewhere for energy because your calorie deficit will be a lot smaller.
The Bottom Line
In other words, your body won't have to look for a lot of extra energy and can make up the difference (between what you burn and what you eat) through other means - body fat.