It’s annoying and its unlikely users will sign up to a newsletter before they’ve actually viewed your site!
Lately I’ve noticed lots of ecommerce sites are doing it.
People search for a product they want to buy, then visit a few websites to compare prices, delivery, service, ratings, etc. They are not going to sign up to newsletters the second they visit those sites.
I suggest you remove the newsletter pop-up and put it somewhere more sensible.