Do people assume you're a serious person?

I guess because of my typically expressionless face, and also my usual lack of emotiveness in my speech, people do. But also, people who are my friends or family who should know me better also think I'm serious too (or at least act all serious around me). This probably has to do with my use of deadpan humor which I don't think many people understand. Then I have to describe to them that I was joking but it still doesn't seem to click with them.

I'm serious when it comes to my hobbies and goals but otherwise I'm a pretty laid back, casual person. Anyone else relate to this phenomenon of being mistaken as serious and any tips to get people to better understand you?