In general, physical activity is better for preventing weight gain than it is for promoting weight loss, and it appears this also applies to yoga.
Most types of yoga don't have the same level of calorie-burning power as aerobic exercise does. Consider that a person who weighs 150 pounds (68 kilograms) will burn 240 calories in an hour of doing regular yoga, compared with 360 calories for an hour of aerobics.
But any physical activity is good activity. Yoga will get you moving, after all, and it can provide health benefits such as improved blood lipid levels and enhanced mood.
Regular physical activity should be part of any weight-loss plan. To lose weight, you want to reduce the calories you take in and increase the calories you burn. If you want to do yoga, the smart play is to include it in an exercise plan that includes aerobic activities, such as biking, jogging or swimming.