It could be allergies. Is your pup doing it on a regular basis like if you get back inside from being outside? Your pup could be allergic to grass, type of food, carpet, etc. You should take your pup to the vet.
My Henry was doing the same including a disgusting snot sneeze once.
I took him to the vet and I have to give him an allergy pill every day. The vet also recommended that I take a damp towel and wipe his paws and beard off whenever I bring him back inside after pottying.