How many? Are they adults? Juveniles? My bin always has 15 - 30 worms traveling the sides and top of the bin, leaving castings in their trails. How's the PH Balance of your bin?

It seems pretty common to hear about worms patrolling the sides and lid of plastic bins. They may just enjoy getting out of bed for a while. If there are still plenty of worms down in/on the bedding, I wouldn't worry too much about it. If it seems that your entire population is trying to escape the bedding, then you by have an issue.
Either too wet
too dry
too acidic
anarobic (not enough air in the bedding)

Sometimes they just enjoy the humidity or the condensation on the lid.

I've never seen worms on my bin lid since the bin is wood and the lid is screen.

Here is a link that might be useful: My Bins

Thanks for the responses, Vermiman and tclynx. So maybe I don't have a problem and these are just worms with wanderlust. There are only about half a dozen or so hanging out up there. Maybe they're just outsiders who want to hang away from the group, looking tough, and dreaming of a different life. I guess they are adults, Vermiman, but truthfully I wouldn't know a juvenile if I saw one (unless they wear earphones and sleep all day). How do you identify the ph anyway, and what is a good one for these guys? Thanks again!
Bene

beneficial: When I first moved my worms from 2 mini-starter bins to the 10 gallon Rubbermaid I had a few that wanted to move UP instead of DOWN. I'd squirt them with the mister and they would return to the bedding.

I think during that 2-week period their habitat was too wet. I added more shredded newsprint, mixed it up and left the cover open for a week and they stopped trying to escape!

My worms don't seem to like their home squeezed-sponge-wet.

Hope yours stopped misbehaving!

Nell