Size of archive, number of "extra" pages, and how frequently you update is going to matter too. My bounce rate is around 30%, but I have a 400+ page archive and a humungous cast. So people will come in, flip through a few recent pages to remind themselves what's going on, visit the cast page because they can't remember who X character is, go to the synopsis page because I've just jumped plotlines, etc. Or they flip back to make sure they haven't missed an update because the schedule has been a little erratic lately.
As others have said, this isn't in itself bad or good, though if you have this sort of comic it is
important to make it easy
for people to find their place. If they start bouncing because it's too much trouble to figure out who character X is or what they're doing, you're going to start bleeding readers quick.
Type of story matters as well. I don't tend to get people linking a single page ala Reddit, Stumbleupon, etc, because they think it was funny and want to share. People link to my pages telling other people to read the story from the beginning. Fewer clicks, but a greater tendency to archive-dive: again, not a positive or negative in itself.
It's useful to look these things over from time to time, but don't fall into the trap of treating it as a measure of success or obsessing over it. Trust me, there are much more useful ways to go insane.