to be up to

به دنبال کاری بودن، قصد یا تصمیمی داشتن

doing something wrong or secret.
When he's quiet like this, I know he's up to ( 1 something.
I wondered what my daughter was really up to.
be up to no good:
I don't know what they're doing but I'm sure ( 2 they're up to no good
Macmillan Dictionary@

be up to sth
:to be doing something
What are you up to at the moment?
Cambridge Dictionary@