MONROVIA, Liberia — Thomas E. Duncan, the Liberian man who developed Ebola symptoms in Dallas after flying from Liberia last month, lied about his history of contact with the disease on an airport questionnaire meant to screen out passengers who might be carrying the virus and is subject to prosecution when he returns, Binyah Kesselly, chairman of the Liberia Airport Authority, said Thursday.

When Mr. Duncan flew out of Roberts International Airport in Monrovia, the Liberian capital, on Sept. 19, he answered “no” to a question about whether he had had contact with any person who might have been stricken with Ebola in the past 21 days, the maximum period of incubation for Ebola, Mr. Kesselly said.

“He lied on his form,” Mr. Kesselly said. “If he had answered truthfully, he would have been sent to secondary screening immediately and not allowed to leave.”

Mr. Kesselly said Mr. Duncan would be prosecuted upon his return.

In a teleconference with reporters, Dr. Thomas R. Frieden, director of the Centers for Disease Control and Prevention in the United States, declined to answer when asked about Mr. Kesselly’s report that Mr. Duncan had lied on his questionnaire. But he did suggest that people often do not understand their level of exposure to infectious diseases.