Introduction - The rising number of COVID-19 cases and deaths led to the implementation of a lockdown for the French population beginning on March 17, 2020. This public health crisis, along with the living conditions during lockdown, is likely to have an impact on the population’s mental health. Santé publique France has therefore established a behavioral and psychological surveillance system aimed, among other things, at assessing the population’s mental health status, identifying its determinants, and monitoring its evolution. Methods - Samples of the general population are drawn from an access panel maintained by the BVA polling institute. In each wave, an independent sample of 2,000 people aged 18 and older residing in metropolitan France is surveyed online. The data presented in this article are from the first two waves, conducted from March 23 to 25 and from March 30 to April 1, 2020. Results - In the first wave, the prevalence of anxiety was 26.7%, a rate twice as high as that observed in a previous survey (13.5% in 2017). In wave 2, the prevalence of anxiety had decreased significantly to 21.5%. A higher risk of anxiety was associated with: 1) sociodemographic characteristics: being female, a parent of a child or children aged 16 or younger, and reporting financial difficulties; 2) living conditions related to the pandemic: working from home during lockdown and having a close relative who was sick or had experienced COVID-19 symptoms; 3/ knowledge, perceptions, and behaviors regarding COVID-19: perceiving COVID-19 as a serious illness and feeling vulnerable to the disease. Conversely, having a good understanding of how the disease spreads, adhering to lockdown measures, feeling capable of adopting protective measures, and having confidence in government actions reduced the risk of anxiety. Furthermore, a decrease in the prevalence of anxiety was not observed among people reporting financial difficulties, those in the most disadvantaged socio-professional categories, or those living in crowded conditions, thus reflecting a widening of health inequalities during lockdown. Conclusions - These initial findings have helped to reinforce and refine the response aimed at promoting mental health and preventing the onset or worsening of psychological disorders. They also highlight the need to protect and support the most vulnerable households. Finally, they suggest that lockdown has a protective effect against anxiety and raise questions about a possible increase in anxiety levels following the lifting of lockdown measures.