The present study investigated whether Japanese 3-, 4-, and 5-year-old children exhibit a yes bias to questions from a physically present humanoid robot, Nao. The robot asked the children yes-no questions about familiar and unfamiliar objects. To both types of questions, the 3-year-old children exhibited a yes bias while the 5-year-old children exhibited a nay-saying bias to questions about unfamiliar objects. The 4-year-old children did not exhibit any response biases. These results were not dramatically different from children's response tendencies toward humans reported in previous studies. The results demonstrate that as children might not spontaneously discriminate a real humanoid robot from humans in social situations, they do not hesitate to answer its questions. Robot usage in education and childcare is discussed.