Antonyms for the phrase "be preoccupied" would include expressions such as "be relaxed," "be free," "be unconcerned," or "be carefree." These terms imply a state of mind where one is not overly occupied or distracted by any specific task or thought, but rather in a more tranquil or idle state. Other antonyms may include phrases such as "be focused," "be attentive," or "be present," which suggest an active and engaged mental state. The opposite of preoccupation is thus a state of being mentally flexible and adaptable, where one is able to concentrate on the present moment and respond appropriately to changing circumstances.