Frank Bwalya, head of the Alliance for a Better Zambia, allegedly referred to president Michael Sata as "Chumbu Mushololwa" during a live radio broadcast Monday.
The Bemba term literally refers to a sweet potato that breaks when it is bent and is used to describe someone who does not heed advice.
"The police decided to arrest and charge him with defamation of the president," Eric Chanda, the secretary general of Alliance told AFP.
If convicted, Bwalya faces a maximum jail term of five years.
