This is tricky. I'm not going to say the answer is No. I do need to caution you in that if an actor is on set trying to stay focused and the director is doing the same, then that is not the time to try to talk to them. Let them do their work. However, there are times (rare) that an actor may want to talk to the extras or a director may want to talk to the extras during the lunch break or some other type of break. That is up to them. If so, then by all means, make the contact and utilize it as a networking experience. Find a way to drop a line about your taking acting classes or your desire to act in front of the camera one day. Encourage them first about the great work they are doing if you are being truthful. Just go with your heart, but stay mindful of the actor/director at work.