(1) What are you doing up there?!
(2) Are you serious?!
Yes: it is possible for an exclamation mark to follow a question mark. This is known as multiple terminals. The question mark signals that the sentence is a question, while the exclamation mark conveys that there was something remarkable about the situation.
Presumably in (1) it came as a great surprise that someone was up there, or perhaps there was an element of danger that was of concern. And in (2) there may have been an element of surprise or disbelief about what was said.