Hi,
You can not dry the ones in the house. You have to let them dry natural on the plants.
Remy

The answer is a little more complicated... The seeds you collected green can be dried and used next growing season, but they will have a reduced germination rate compared to those which matured on the plant.
If you don't have the option, then just go for it, otherwise use seeds matured on the plant.

I would recommend against it for saving the seed. Being LousianaGardener says they are still moist, I'm assuming they are not at the end stages of ripeness. If they are moist, they will become shriveled and be of no use for next year. Now if the seeds were almost ripe with an outer shell that was starting to dry and the cowpeas were pretty firm and almost ripe. I would say give it a shot. The germination rate would be lower, but you would have some successful germination next year.
So waiting just a little longer on the pods on the plants is so worth it for saving the seeds.
Remy