What have you been up to?

Her (2013)

What have you been up to?

Actually, I was talking to someone I just met.

"What have you been doing?" has same meaning with "What have you been up to?"

The Big Bang Theory (2007) - S11E17 The Athenaeum Allocation

What have you been doing?

It's 8:00 a.m. Sleeping.

And this,

Friends - The One That Could Have Been: Part 1 [S06E15]

                 So what's going on with you?

                        Well, um, I've been doing a lot more of my karate.