Asexuality is a sexual orientation characterized by the lack of sexual attraction towards people in general. Asexuals may or may not be interested in romantic relationships, but are not physically drawn towards sexual activity. They may choose to live celibately, or to participate in sexual activity for practical considerations, so asexuality and celibacy are two very different things.
Is an asexual person obligated in the mitzvah of Pru Urvu despite not experiencing sexual attraction at all? On the one hand mitzvot are normally obligatory even when one does not want to perform them. On the other hand, perhaps the psychological damage that would be incurred by forcing this person to have children would exempt them. Furthermore, perhaps the commandment is contingent on the presence of sexual attraction in the first place, as suggested by an anonymous source here (the key claim is that "If a person’s psychological infrastructure was such that it didn’t attract him to women, he is not obliged to steel himself and live in a marital relationship in order to have children.").