If you say no, most interviewers will keep drilling deeper to find a conflict. The key is how you behaviorally reacted to conflict and what you did to resolve it. For example: "Yes, I have had conflicts in the past. Never major ones, but there have been disagreements that needed to be resolved. I've found that when conflict occurs, it helps to fully understand the other person's perspective, so I take time to listen to their point of view, and then I seek to work out a collaborative solution. For example . . ." Focus your answer on the behavioral process for resolving the conflict and working collaboratively.