'what are you up to?' = what are you doing? or what is happening here? When spoken, it can have secondary meaning, depending on how it is said. - It can have a negative connotation, implying that the questioner feels someone is concealing an action or conspiracy. - It can have a positive meaning, when asked in a friendly way, so that is more 'are you doing something interesting?' - It can be a scolding statement, an admonishment - 'what ARE you up to?' The previous question? I think you are probably trying to say "what is the meaning of this question?"

"What are you up to?" simply means "What are you doing right now?"

It can also be a very general conversational question, like 'what's happening?' 'what's going on?' 'what's up?' I think either you say these things whaen there is something obviously happening, in which case it means 'what is the explanation?' But if there is no obvious big thing happening, then it is jsut a general inquiry about what's new or interesting. You may also know a familiar dialect version of 'what's up?' that's pronounced 'whassup?'