There is a small amount of fat in Cocoa Powder, so it could theoretically go rancid. It would take a good long time, though -- more than three years I would think, unless it was poorly stored.
Thanks. I checked the carton and there is no expiration date on it. I'll give it a sniff. Hopefully I can tell if it is expired. I'm the worst at smelling things to determine if they're past their time.