Background noise is often discussed in terms of mental costs. In this study the effect of background noise on brain activity as reflected by the direct coupled (DC) potential was investigated by a within design in ten participants. During two successive blocks of 7 min each, participants performed 156 trials of a visual display terminal (VDT)-based visual-spatial attention task without noise and two blocks with a mixture of the environmental noises of barking dogs, traffic noise and irrelevant speech of 60 dBA. Brain DC potentials were recorded along the midline and analysed for change by time on task. For noise conditions, reaction time was prolonged and the DC-potential shifted towards positivity, contrary to control condition, independent of block and location. Results suggest reduced cortical resources by widespread inhibitory activation through background noise. It can be concluded that even low intensity background noise is associated with energy consumption and with impaired performance in spatial attention.