The items, valued at Â£15,000-Â£20,000, were part of a 12-place setting of dining cutlery dating from 1902.
Proceeds from the auction, to be held at Lyon & Turnbull in Edinburgh next week, will go to The Willow Tea Rooms Trust in Glasgow.
The tea rooms at 217 Sauchiehall Street were taken over by the trust in 2014.
The cutlery set was originally commissioned by Glasgow Girls artist Jessie Newbery and her husband Fra in 1902 as a gift from her parents.
The commission was handled by jeweller Edwards & Company in Glasgow and made by DW Hislop, a local silversmith who worked with Mackintosh on other projects.
Each set contained a soup spoon, dessert spoon, dinner fork and dessert fork, with knives supplied separately from a stock pattern.
All of the pieces were later divided equally between the Newberys' daughters Mary and Elsie, with Mary's cutlery sold separately during the 1970s and 1980s.
The silver fork and spoon were donated by Celia Sinclair, founder and chairwoman of The Willow Tea Rooms Trust.
She said: "I am delighted that I am able to offer these beautiful objects for sale to benefit the work we are doing at the trust. The money raised from the sale will go towards the restoration of the tea rooms."
Renowned as the most elegant of Miss Cranston's four tea rooms, the Willow Tea Rooms opened in October 1903, with Mackintosh at work designing it from the beginning of that year, if not earlier.
The trust purchased the premises in July 2014 and as well as restoring the tea rooms, it plans to incorporate a visitor centre to celebrate the building and other works by Mackintosh.
It will also highlight the achievements of Miss Cranston, an early female entrepreneur.
John Mackie, decorative arts specialist at Lyon & Turnbull, said: "I greatly admire the work the trust has undertaken to ensure the legacy of Mackintosh will be here for future generations to enjoy."
The fork and spoon will go under the hammer on October 26.
A silver fork and spoon designed by Charles Rennie Mackintosh are to be auctioned to help restore tea rooms which he also created.