The 38-year-old said in her Twitter post that she did not believe that her husband wrote the note.
She tweeted: "Here is the alleged suicide note found in John's pocket,
"This note does not sound anything like someone who has no hope and is contemplating ending their life.
"This note sounds like one of John's tweets. #NotASuicideNote #JusticeForJohnMcAfee."
Janice - who married John in 2013 - also claimed: "The handwriting is suspect & I doubt the authenticity of the note.
"It reads more like someone trying to imitate John's style of tweeting. And if this note was found in his pocket where are the markings of the note being folded into his pocket? #NotASuicideNote #JustForJohnMcAfee."
McAfee was found hanging in his cell in June, with an autopsy ruling that he had killed himself. He was awaiting extradition to the USA.
Whilst some parts of the note have been scribbled out, the words that can be read state: "I am a phantom parasite,
"I want to control my future, which does not exist."
Despite the ruling from Spanish officials that McAfee killed himself, his wife has consistently argued that he was not suicidal.
"His last words to me were 'I love you and I will call you in the evening,'" she told reporters outside the prison near Barcelona where she recovered her husband's belongings.
She added: "Those words are not the words of somebody who is suicidal."
Mrs McAfee has also accused the Spanish officials of a 'cover-up' after she did not receive 'the death certificate, the official autopsy report, or the official report from the prison.'
"I understand that things take time but the lack of cooperation from the Spanish authorities only confirms our suspicions that they have something to hide," she said.
She has also said that she was allowed to see the body of her late husband, but that she could only view his 'head through a window at the facility where they are keeping him,'
"His entire body from the neck down was covered with a sheet & blanket."
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