"Keyed up" is an expression used to describe being nervous, anxious, or excited. Some antonyms for the phrase might include "calm," "relaxed," "composed," "tranquil," and "serene." These words all suggest a state of being free of nerves or worries, and instead feeling at ease, content, or peaceful. Other antonyms for "keyed up" might include "unconcerned," "nonchalant," and "indifferent," which suggest a lack of interest or emotion in a given situation. Ultimately, the antonyms for "keyed up" all describe a state of mind that is opposite from the jittery or frenzied feelings that the initial phrase connotes.