Some of the letters have already received bids, with the letter about Trump's Taj Mahal casino, already receiving a bid of at least $1,330.
In the letters to her companions, Lee gives her thoughts to a number of subject matters, from Broadway productions and other novelists, to her own health and well-being.
"These letters offer fascinating insight into Harper Lee's life (and) her correspondence with her friends since she was notoriously known as a private person," Samuel Heller, Nate D. Sanders Auctions' PR director, told CNBC via email.
"The auction house is already thrilled with the reception the letters have received. Harper Lee letters are highly coveted by collectors especially after the release of her new book and her passing last month," Heller added.