Yes. Catabolism is the process by which the body breaks down stored energy for fuel. This can be muscle, fat, even bone is affected by catabolism.
However, what I think you are referring to is the question, "Does taking a diet pill make me lose muscle?"
The answer there is: maybe. The vast majority of diet pills rely on caffeine as a primary ingredient, which is known to cause the release of cortisol, which in turn can stimulate proteinolysis. But, if you don't starve yourself and instead diet wisely, recover from your workouts sufficiently, and don't overdo your caffeine and stim intake, your cortisol levels should remain within an acceptable range.
Just don't cut cals too much, or overstim yourself and you should be fine on a diet pill.