The antonyms for the word "be mischievous" are numerous. Some of the opposite words for this term are responsible, honest, upright, virtuous, blameless, conscientious, decent, ethical, good, honorable, lawful, moral, noble, and upright. These antonyms articulate the opposite qualities of a person who is not mischievous, such as displaying ethical behavior, being responsible, being virtuous, and maintaining a high level of morality. Such people often act in a trustworthy manner, and they do not engage in activities that are considered deceitful or harmful to others. Essentially, the antonyms for "be mischievous" reflect positive characteristics that individuals should strive to embody in their lives.