I have a job offer (Account manager) and the employer (Marketing Company) is going to sponsor my visa, but there is a concern that the visa will be declined because my qualification is a bachelor Degree in Mechanical Engineering.
HIB visas are reserved for employees of companies with highly specialized knowledge relevant to their employment. The fact that your degree was in mechanical engineering will not disqualify you from an HIB visa for an accounting position if you can demonstrate that you have developed specialized expertise in this field. You will need to work with an immigration attorney who can prepare your application with care.
As you probably now, the number of HIB Visa applications each year is far greater than the number of slots allowed by Congress. Thus, among those who otherwise qualify for the visa, there is a lottery, and many who qualify fail to get the visa. This is a hard visa to obtain even if you clearly qualify. I would need to know a lot more about your personal situation and the job which you have been offered to give you advice as to the likelihood that you quality, but chances are the problem for you will not be whether you qualify.
You should know that there is particular scrutiny these days of whether there is a true employer employee relationship. Generally speaking, you will be required to work on the premises of your employer, and the position must in all respects appear like a traditional employer/employee relationship.
The general advice you receive on this web-site is no substitute for working with qualified immigration counsel. Many companies who legitimately need to sponsor an HIB worker will pay the costs of immigration counsel. Even if your company will not pay the fees of immigration counsel, you would be well-advised to do so and,moreover, to develop a long term relationship with immigration counsel. You will no doubt need help from such counsel on a continuing basis over the coming years.