Interviewers usually pose this question because they may be interested in knowing how serious you are in pursuing a given academic or professional field. In an internship context, this question should compel you to dig down and think about your career interests in the long term: Are you planning to go back to graduate school? Are you interested in gaining a few years of actual real-world experience? Would you like to work as a full-time staff member of an organization similar to the one you are applying for? There is no “right answer” but you do have to provide one that is insightful in that you have a plan to keep building your professional skills after your internship. Who knows, maybe your organization would like to know if you would be available for a permanent position after you complete your internship. And in that case, how you answer this becomes all the more important.