Jealousy is a negative emotion, right, so distance yourself from this person. Remove any negative energy from your space immediately. It doesn't matter if this is your blood or an acquaintance. A jealous person does not want the best for you.. they want whatever it is that you have, and sometimes, they will try and take it from you.
Depending on the type of relationship you have, its always good to communicate your observations, thoughts if you do decide to distance. However, its not always necessary.