One reason to consider getting an MBA is you will receive opportunities to network with future colleagues and business contacts during your time in school, or you may become eligible for a promotion within your current company.
You may want to stay with your bachelor's degree if you are looking only for an increase in salary. A master's degree in business does not always increase a person's salary enough to justify the cost of the additional years in school.
You may find out that your employer is willing to pay for you to get a master's degree in order to keep you in the company.
Decide whether you have the time for a master's degree in business. If you already work full time, you will probably have to go to school part-time, which means your degree will take longer to complete.
If you have a bachelor's degree in another field, a master's degree in business may work better for you than going back for another bachelor's. Business master's programs are usually open to accepting students from other fields.