Hi Mitra. I have an MBA and my undergraduate degree is in Accounting. However, plenty of my friends have undergraduate degrees in Journalism, History, etc. and still got into prestigious MBA program. So I believe the answer is no, you don't have to.
I studied overseas before I moved to the States, Recently I looked into getting my MBA too. My research with the various Universities was a mixed one. Some preferred you to have a business major (especially those that you attend full time). Since I have a full time job also, I looked at getting my MBA online and I noticed that many of them did not require a business major, there are 2 options: 1. take the pre-req. online classes prior to the start of the MBA or 2. provide enough documentation that you have X yrs of hands on business experience (the X varies by university)
Ritesh recommends the following next steps:
Alghough I do not have direct experience, here is a good answer for this question.