Sirleaf was speaking Thursday in an exclusive interview with CBC News senior correspondent Adrienne Arsenault.
"With the U.S. doing so much to help us fight Ebola, and again one of our compatriots didn't take due care, and so, he's gone there and … put some Americans in a state of fear, and put them at some risk, and so I feel very saddened by that and very angry with him, to tell you the truth."
Sirleaf also disclosed that the man, identified in U.S. reports as Thomas E. Duncan, worked in the private sector with courier company DHL.
She said the man had passed temperature tests, and "some very stringent precautionary measures" at the Monrovia airport.
"But the fact that he knew [he was exposed to the virus] and he left the country is unpardonable, quite frankly," she added. "I just hope that nobody else gets infected."
She suggested she'll have to consult lawyers to decide what to do with the man when he returns home.
Sirleaf, 75, has been president since 2006. She is the first female head of state elected in Africa.
Sirleaf won the Nobel Peace Prize in 2011, jointly with Leymah Gbowee of Liberia and Tawakel Karman of Yemen. All three were praised for their struggle for the safety and political role of women.
"In her efforts to bring justice to her people in Liberia, she has spent more than a year in jail at the hands of the military dictatorship of General Samuel Doe and had her life threatened by former President Charles Taylor," the Nobel Prize website says.
She holds a degree from Harvard University's Kennedy School of Government.