be up to something

[smartie_Warsaw]

Hi,

can you tell me what it means?

thanks a lot

 

[Horsa]

If somebody "is up to something", it usually means they are doing something (or are suspected of doing something) underhand or mischievious.

 

[Ouisch]

It means to be planning or plotting something.

"My mom hasn't mentioned my upcoming birthday at all. I wonder if she's up to something. Maybe she's planning a surprise party?"