I think my thinking of 'Active' depends on what size the RP Group is.
I've seen many Lion Prides lately and they seem to have tons of members. So if it's a group of that size my meaning of active is for around 10 people to be online each day.
But I've also seen and been in many small RP groups. So for a group of that size I'd expect either everyone or no one to be online.
Site updates are also another large aspect of the term 'active' in FeralHeart. As many groups have their own site, They can tell people to get online if they haven't been for the past few days. but as for Site Updates, I don't expect one every other day as people can be busy to keep updated with the site and such.
For RolePlay days this is very important, Seen as you're talking about activeness for a RP Group. I'd say 2-3 days every week would be a roughly good time for people to RolePlay.
Overall I think activeness depends on the size of the group and the type of people in it. As some people can be busy due to work and school.