Writing on his official website, the entertainer warned that the rumour might be a computer virus.
He continued: "And now ladies and gentlemen for my rebuttal. As you well know, a dead person cannot rebuttal. Therefore, I am rebuttaling to tell you that when I heard the news I immediately began rebuttaling and went into denial.
"My wife has just informed me that there is no such word as rebuttaling, she says the word is rebutting. But I don't care, because I'm alive!"
Cosby concluded: "Thank you. PS - that's another thing dead people don't say."
Johnny Depp was also recently the subject of an online death hoax.