It could be frost damage, since I notice that there are healthier leaves further down. My killing freeze is very late this year (not that I'm complaining, mind you), but there were a couple light frosts this week, and the few beans that still have foliage look very much like yours.

There is probably no cause for concern. Most beans are winding down at this time of year anyway, if they are not already dead. I would recommend checking the underside of the leaves, but chances are that both your compost & your seeds are safe.