Yes you can!
Unless you mean filling the cracks between the boards. If so, I wouldn't do that. In general, they should not be filled.
But, If you have damaged wood that needs repairs:
Mix the sawdust with enough wood glue until until you get a putty consistancy. Then apply like ordinary putty. If it shrinks when dry, you may need to add more putty to fill larger holes.
This usually is a very good match to the wood and is sandable after drying.