His lawyer Emmanuel Simh confirmed his client was jailed at the capital Yaounde's central prison ahead of his first hearing at the Yaounde administrative centre.
"I did not have access to his file, but he is prosecuted for apology for crime, contempt and assault threats," he told AFP, adding that the charge of "contempt of the President of the Republic" and "forgery and the use of forged documents" had been dropped.
Nganang, who teaches literature at New York University, was arrested on December 6 in Douala, the economic capital of Cameroon, on his way to fly to Harare in Zimbabwe.
Cameroonian government spokesman Issa Tchiroma Bakary said that the writer had made threats against President Paul Biya on December 3 on Facebook.
Nganang is alleged to have written that he had a gun and that he was going to shoot Biya in the head.