I use “up to” often in my conversations.
“What are you up to this weekend?”
“I’m not up to anything. Do you want to see a movie?”
“What is your brother up to?” (Meaning, what is he doing right now.)
“Nothing. He’s as home watching TV.”
“You’re being quiet. Are you up to something?”
“Yes, I am.”
So, what are all of you up to this week? I’m taking some time off from work.