<i>Background/Aims:</i> The present study investigated cortical correlates of top-down processes in visual-object working memory with multi-channel near-infrared spectroscopy. <i>Methods:</i> The activity of the prefrontal cortex (PFC) was investigated while performing an n-back task with sequentially presented task-relevant and task-irrelevant faces. The activation patterns in the PFC associated with working memory and interference resolution were examined in 20 healthy adults. <i>Results:</i> We found a bilateral enhancement of oxygenated haemoglobin in the lateral PFC for remembering relevant faces and in the right lateral PFC for ignoring irrelevant faces. Oxygenation for relevant and irrelevant faces did not differ significantly, indicating that memory pro- cesses and interference resolution were interdependent functions, which were subserved by comparable prefrontal regions. <i>Conclusion:</i> This supports the notion that the prefrontal activity during working memory tasks reflects not only maintenance processes but also attentional monitoring and selection processes.