Mars atmosphere

Please forgive a stupid question, but my curiosity got the better ofme. I was
reading that duing a Mars summer, the temperature hits around 70 degrees. Would
it theoretically be possible for a human to venture onto the Mars surface in
these temperatures, in more or less shirtsleeves, using only an oxygen mask?
Just for a short term, or maybe not. Like I said, a stupid question, but given
the Earthlike temperature, it got me wondering. Thanks.