Tell him to grow up and not worry about it. You were just talking is all. Jealousy like that is immature. He'll get over it. I would keep an eye out though because if someone gets mad at something innocent like that, there could be worse episodes to come.
Tell him to stop, and that he doesn't have a reason to be mad at you if you were just talking, and that you don't even like him. Him being really jealous isn't always a good thing because, in the future if you 2 are together there could be problems. What if you work with another boy and have to talk to them? He might not like it get mad, and then you get upset, don't want him to be mad at you and quit your job. He (in my opinion) needs to man up. If he can't stand to see you around other guys than maybe he's just not for you. :) Hope this helped.