Sleep deprivation has become a severe public health problem in modern societies. Negative consequences of prolonged wakefulness on cognitive abilities have been demonstrated and working memory is one of the main cognitive functions that can be affected by sleep deprivation. This study aims to investigate the effects of sleep deprivation on working memory through EEG event-related oscillations. Thirty healthy young adult university students and graduates were included in this study (15 rested control – 15 sleep-deprived). A 2-back task was used to evaluate working memory, and both groups performed the task during EEG recording. The sleep-deprived (SD) group was required to stay awake for 24 h, and then the EEG session was conducted. The rested control (RC) subjects participated in the morning after a regular night’s sleep. Event-related power and phase-locking analyses were applied, and delta (1–3.5 Hz), theta (4–6.5 Hz) and alpha (8–13 Hz) frequencies were investigated in the time-frequency domain. In the 2-back task, significantly prolonged reaction times were observed in the SD group. However, the decrease in accuracy rate was not significant. The EEG analyses revealed that the SD group had decreased frontocentral event-related delta and theta power responses after the presentation of stimuli. Moreover, task accuracy was positively correlated with the left frontocentral delta power in the SD group, and theta power in the RCs. Thus, we propose that the adverse effects of sleep deprivation on working memory can be observed through low-frequency oscillatory responses in the brain.