(1) Background: The Berlin questionnaire (BQ) is a widely used survey to predict obstructive sleep apnea (OSA). Considering the confounding effect of obesity and hypertension on the clinical course of COVID-19, we have recently developed a modified BQ (mBQ) based on the subscales snoring intensity/frequency, witnessed apneas and morning/daytime tiredness, and demonstrated that patients with high-risk OSA had worse outcomes during the COVID-19 pandemic. In the current study, we aimed to validate the mBQ in adults with a history of COVID-19 infection. (2) Method: All cases who suffered from COVID-19 infection between 10 March and 22 June 2020, and who completed the mBQ in our first study, were invited to participate. Participants refilled the questionnaires, and an attended polysomnography (PSG) was conducted. An apnea−hypopnea index (AHI) of 15 events/h or more was considered as OSA. (3) Results: Out of the 70 participants, 27 (39%) were categorized as having a high risk of OSA based on the mBQ. According to the PSG results, 24 patients with high-risk OSA (89%) and 3 patients with low-risk OSA on the mBQ (7%) had AHI ≥ 15 events/h. The mBQ had a sensitivity of 89%, a specificity of 93%, a positive predictive value of 89%, a negative predictive value of 93%, and an accuracy of 91%. The area under the curve was 0.91 confirming a very good performance of the mBQ in screening for OSA. (4) Conclusions: The mBQ has a good level of diagnostic sensitivity, specificity, and accuracy among adults with a history of COVID-19 infection. Since the confounding effects of obesity and hypertension are eliminated, the mBQ may be used not only as a screening tool for high-risk OSA but also as a prognostic survey in clinical cohorts.