Hey hswoo,
It all depends on what type of MBA you plan to peruse. Most MBA request that you have 3 or more years of work experience, less than that may make it difficult to show that you have enough experience, leadership, team work knowledge in the workplace to contribute to e program. You can apply with less, but it will be tougher to prove your abilities. Many applicants will have over 3 years.
If you choose to work while earning an MBA, studying part-time, many of the applicants have over 5 years. And if you choose to peruse an executive MBA, you typically need a min of 5-7 years, at least 3 of which should be in a management position.