The tennis coach said Murray, who won gold in the men's singles at London 2012, would probably find the experience "emotional".
Andy Murray is due to lead Team GB at the opening ceremony of the 2016 Olympics at 00:00 BST on Friday.
The current Wimbledon champion is the first tennis player to fill the role.
Judy Murray told BBC Scotland's Good Morning Scotland programme that representing his country in Rio was a true honour for Murray.
She said: "It's absolutely amazing. Obviously the Olympic Games is the biggest sporting spectacle in the world and to be able to carry the flag for your country, obviously it doesn't get any bigger than that. I know he's absolutely thrilled to bits and probably just a little bit nervous as well."
She said that being part of a team and sharing the occasion with other athletes was also something that Murray embraced.
She added: "Everyone can see from the way that he approaches the Davis Cup that he loves representing the country.
"He loves team competition and I know that when he was at the Olympics in London, particularly that whole sense of being part of a much bigger thing than just tennis, it was the whole British team - the crÃ¨me of our sporting athletes - it was a massive, massive thing for him."
She added: "He's been through Beijing and London. He kind of knows what it's all about and so he has a much bigger sense of the duty and the occasion and of course the opportunity, so I think he's going to find it a little bit emotional."
Despite being a regular fixture courtside when Murray plays, his mother said she would not be in Rio for the Games and would instead be in Granton-on-Spey with her Tennis on the Road programme.
Judy Murray has said her son Andy is "absolutely thrilled" to have been chosen as flag bearer for Team GB at the Rio Olympics.