Working memory is a fundamental cognitive brain function enabling us to hold transiently and process sensory information for a future goal. The prefrontal cortex was long thought to be the specific site for working memory in mammals. However, there is growing evidence that parallel distributed circuits may be responsible for working memory stressing the importance of sensory cortices for the active maintenance of information in working memory. The specific functions of working memory representations in sensory versus associate areas remains unknown. One possibility is that associative areas contain representations that are more abstract. Another possibility is that working memory-related activity emerges simultaneously in sensory and associative areas under the control of the bidirectional connections between these areas. Here we established a auditory delayed non-match-to-sample task in head-fixed mice. After more than 1 month of training, mice performed the task above 70% accuracy for an inter-sound interval of 1.5s showing their ability to remember sound information well after the stimulus is terminated. We recorded from large populations of auditory cortex neurons using in vivo 2-photon calcium imaging during behaviour using the fast calcium reporter GCAMP8m. We observed a robust representation of sounds by neuronal population following during the early part of the delay period at least up to 500ms after sound offset both in naïve and trained animals. These representations could seed the maintenance of short-term sound memory over time.