This study aims to examine the public interest that exists on internet regarding various mental health topics and its relationship with evolution of COVID-19 pandemic in Spain. Google Trends was used to explore relative search volume (RSV) for the following terms related with mental health (TRMH): "anxiety", "depression", "stress", "insomnia" and "suicide"; between January and December 2020. The cross-correlation function was performed to assess association between new COVID-19 cases and RSV levels for TRMH. Finally, Mann-Whitney test was used to examine differences between RSV values for TRMH before and after of state of alarm declarations on March and October 2020. The "anxiety" term showed the highest RSV indices. A significant correlation was found between new COVID-19 cases and RSV for "anxiety" with a time-lag of +1 week (r=0.49; p<0.05). Was found an increase of SRV for "anxiety" (U=0.00; p=0.01) and a decrease of SRV for "depression" (U=1.00; p=0.04) between 4-week period before and after state of alarm of March 2020. Regarding the state of alarm of October 2020, a higher RSV for "anxiety" (U=0.50; p=0.02) was found in the four weeks after it compared with a similar previous period. Anxiety is the mental health topic of greatest public interest on internet in context of COVID-19 pandemic. Public concern about anxiety rises one week after the increase in COVID-19 cases and is greater after introduction of control measures that entail any type of mobility restriction or activity limitation. There is a greater general need for information on anxiety at specific times in the pandemic evolution. Copyright © 2021 SEP y SEPB. Publicado por Elsevier España, S.L.U. All rights reserved.