Visual backward masking (VBM) is a very sensitive endophenotype of schizophrenia. Masking deficits are highly correlated with reduced EEG amplitudes. In VBM, a target stimulus is followed by a mask, which decreases performance on the target. Here, we investigated the neural correlates of VBM in unaffected siblings of schizophrenia patients. We had three conditions: target only and two VBM conditions, with long and short inter-stimulus intervals (ISI). Patients’ performance was impaired, while the siblings performed at the same level as the controls. Interestingly, EEG peak amplitudes were higher in siblings compared to controls, while they were lower in patients relative to controls as previously reported. For siblings, EEG amplitudes were at the same level in all conditions. For controls and patients, EEG peak amplitudes increased with task difficult, e.g., amplitudes in the long ISI condition were lower than in short ISI condition. Our results suggest that unaffected siblings of schizophrenia patients use a compensation mechanism tuning the brain to maximum performance in all conditions. Since siblings are already at the peak of their activations, increasing the task difficulty does not change brain processing.