What are you up to?
→지금뭐하는거니?

※be up to (어떤일)을 하고있다.계획하다
  (=What are you going to do?, What will you do?)

〔예문〕
A :What are you up to, Tony?
   토니, 지금 뭐하는거니?

B:Nothing. I'm just shopping.
  아무것도 않해. 그저 쇼핑할뿐이야.