This is a leading question. If you have been called for an interview it is unlikely the employer considers you greatly over qualified. Otherwise they could not justify the time spent interviewing you. Do not apologies for your degree. Rather state your willingness to start at the bottom and work your way up, your enthusiasm for the organization and your desire to develop a broader range of skills. Emphasize skills such as fact finding, analysis, your capacity to acquire new knowledge quickly, rather than the specific content of your degree. Some employers are more interested in what you can offer in the ‘practical hands-on’ sense than in the ‘academic’ sense!