Behavior-based architectures use behaviors as building blocks for decision-making and action execution processes. Behaviors are distributed and evaluated in parallel for the control of the robot, taking real-time inputs from sensory data and sending real-time commands to effectors. No centralized components exist in these architectures, each module carrying out its own strategy independently, making an overall behavior emerge from the interaction between the concurrently executed modules and the environment. In this paper, we discuss the use of a reactive hierarchical task network (HTN) planner in a behavior-based robot architecture. The planner in this architecture is not a central component on which everything else relies on, but acts as one of the motivational modules recommending tasks to be executed and influencing the selection and configuration of behaviors. The planning module allows the behavior-based architecture to deal with tasks with priorities, flexible time constraints and on-line planning using a simple but very effective reactive planning strategy. We demonstrate our approach in the context of making a robot attend a conference.