Possibly. But I've read that yellow leaves mean the plant needs more iron, which can be solved with a good, balanced fertilizer. It's a good idea to closely inspect the plant for other problems, though, such as fungus or tiny insect infestations, both of which could make the plant sick enough to drop its leaves. Another problem might be a lack of sufficient humidity, or that when you water, only the soil (and not the plant roots) are getting soaked. Ficus should stay healthy down to 50 degrees F...I would double-check all these details and take it to a nursery for advice if nothing helps.