Yes it is natural for all dogs because they want to protect their young. I would not get too close but if she doesn't let you near them in the next few days to check on the litter then I would suggest to try and bait her with a treat or something or ask a professional on a Veterinarian website.
Since my pug had puppies, she's been extremely needy and attention seeking of humans them mean to our other dogs. She also has taken control of several laundry baskets and just sits in them, for hours.
Your dog is just trying to protect the puppies. If you had a child wouldn't you try to protect him/her? It is the same thing with your dog. She is just overprotected. Wait a bit and she will eventually let you near the pups :) Congrats on the litter!