The true intentions of humans are sometimes difficult to ascertain exclusively from explicit expressions, such as speech, gestures, or facial expressions. In this experiment, functional magnetic resonance imaging (fMRI) was used to investigate implicit intentions that were generated while a subject was reading self-relevant sentences. Short sentences, which were presented visually, consisted of self-relevant statements and a substantive verb, which indicated sentence polarity as either affirmative or negative. Each sentence was divided into the contents and the sentence ending, and the subjects were asked to respond with either agreement or disagreement after the complete sentence was presented. The overall group analysis suggested that the intention of the sentence response was found even before the reading of the complete sentences. Increased neural activation was found in the left medial prefrontal cortex (MPFC) during feelings of agreement compared to feelings of disagreement during self-relevant decision-making. In addition, according to the sentence ending, the decision of a response activated the frontopolar cortex (FPC) in the switching condition. These findings indicated that the implicit intentions of responses to the given statements were internally generated before an explicit response occurred, and, hence, intentions can be used to predict a subject's future answer.