“We've just been catching up with each other.”
You and your husband are visiting a couple that you haven't seen in a long time. You and the other woman have been talking together for a few minutes while your husband and the other man talk to each other. Your husband wants to re-join the conversation between the men and women, so he asks how you're doing. This is your response.
We've just been catching up with each other.
Use "has been ___ing" to talk about something that started in the past, continued without stopping or happened again and again, and is still going on now:
You've been sitting there at your computer for over two hours.
I've been designing web pages for over ten years.
Or you can use it for a situation that you're not sure whether it's finished or it's going to continue:
It's been cloudy all morning, but it looks like the sun might come out soon.
If it's already understood who you're catching up with, you can just use the phrase "catch up":
We're just catching up.