There isn't a right or wrong answer to interview questions about what motivates you. The interviewer is trying to understand the key to your being successful in the job he is interviewing for, and wants to make sure it's a good fit. Consider, in advance of interviewing, what actually does motivate you and come up with some specific examples to share during the interview.
Your response will vary based on your background and experiences, but, you will want to share your enthusiasm and what you like(d) best about your job. Here are some examples:
I was responsible for several projects where I directed development teams and implemented repeatable processes. The teams achieved 100% on-time delivery of software products. I was motivated both by the challenge of finishing the projects ahead of schedule and by managing the teams that achieved our goals.
I've always been motivated by the desire to do a good job at whatever position I'm in. I want to excel and to be successful in my job, both for my own personal satisfaction and for my employer.
I have always wanted to ensure that my company's clients get the best customer service I can provide. I've always felt that it's important, both to me personally, and for the company and the clients, to provide a positive customer experience.
I have spent my career in sales, typically in commission-based positions, and compensation has always been a strong factor in motivating me to be the top salesperson at my prior employers.