Hi Flavia, It means that someone is interested and enthusiastic in doing something. Example: Joe was keen on the idea of a road trip. Cheers, Lance

On a personal level to be keen on someone means to fancy them, to want to go out with them

To be keen on something means to be very interested on something. To put time, effort and interest on something that you like for example. You can be keen on learning languages.

It can also means "to be interesed"

It means to like something or be enthusiastic about it.