The Franklin & Bash star recently popped the question to McGuinn with a ring designed by jeweller Neil Lane, reports People.
The engagement band was a custom five-carat cushion-cut diamond ring, which Lane designed specifically for him.
"He couldn't wait to propose. He was so excited to have found the woman of his dreams," Lane told the publication.
No date for the wedding has been decided upon yet.
Gosselaar split from ex-wife Lisa Ann Russell in June 2010.
The former couple have two children together, 7-year-old Michael and 5-year-old Ava. Gosselaar recently filed for joint custody following the finalisation of his divorce from Russell.