"We have to warn Matt and Trey that what they are doing is stupid and they will probably wind up like Theo Van Gogh for airing this show," warned the posting, written in the name of Abu Talhah Al-Amrikee.
"This is not a threat, but a warning of the reality of what will likely happen to them," it added.
Mr al-Amrikee later told the Associated Press the posting was not an incitement to violence. It had been published to raise awareness of the issue and to see that it did not happen again, he added.
A Comedy Central spokesman said the network had no comment.
In the 200th episode of South Park broadcast last week, Muhammad appears several times inside a bear suit. The prophets of the other main religions are also depicted, including a drug-snorting Buddha.
http://news.bbc.co.uk/2/hi/americas/8636455.stm