Introduction: We investigated the longevity of COVID-associated brain fog in patients who have survived the COVID-19. Methods: This was a follow-up study of 2,696 adult patients with COVID-19 from our previous study. We selected every other patient in our database. The follow-up data were collected during a phone call to the participants in January–February 2022 (11 months after the initial study): concentration difficulty and the patient’s self-declared status in their ability to concentrate. Results: In total, 1,164 people were included; 35 people (3.0%) had concentration difficulty and 65 individuals (5.6%) had a worsened status in their ability to concentrate and think; 26 people (2.2%) responded yes to both questions and were considered as having long-lasting brain fog. People with long-lasting brain fog were more often admitted to ICUs during the initial hospitalization (23.1% vs. 9.3%; p = 0.032) compared with those without long-lasting brain fog. Conclusion: We may conclude that a minority of the hospitalized patients with COVID-19 may suffer from long-lasting post-COVID brain fog, at least for more than 1 year after their initial illness. Long-lasting post-COVID brain fog has a significant association with the severity of the initial illness.