The phrase "being off mark" refers to something or someone being inaccurate, imprecise, or incorrect. There are various antonyms that can be used to describe the opposite of being off mark. These include being accurate, precise, correct, exact, meticulous, and on target. These antonyms indicate a sense of correctness, attention to detail, and accuracy. Being on the mark implies that a task or objective has been completed successfully and to the required standards. Such antonyms highlight the importance of precision and accuracy in various aspects of life, including professional, academic, and personal pursuits, and the need to strive towards achieving them.