The health and socio-economic challenges arising from the COVID-19 pandemic have led to greater reliance on the internet to meet basic needs and responsibilities. Greater engagement in online activities may have negative mental and physical health consequences for some vulnerable individuals, particularly under mandatory self-isolation or ‘lockdown’ conditions. The present study investigated whether changes in levels of involvement in online activities during the COVID-19 pandemic (i.e., watching TV series, online sexual activities, video games, social networks, gambling, online shopping, and instant messaging) were associated with problematic internet use, as well as whether certain psychological risk factors (positive/negative affect and impulsivity) were significant predictors of these changes. A total of 1,275 participants (66.1% female, aged between 18-55 years) completed an online survey while in lockdown in Spain (April 15th-23rd, 2020). The survey assessed current engagement in seven different online activities and their engagement prior to the COVID-19 pandemic, as well as psychological risk factors (affect and impulsivity). Most participants (between 60.8%-98.6% depending on the activity) reported no changes in participation in online activities, but there was a significant increase in weekly internet use (between 25 and 336 min). However, increased internet use was not accompanied by a corresponding increase in problematic use, except for problematic TV series watching and video gaming. Psychological risk factors considered in the study (affect, impulsivity traits) were largely minor or non-significant predictors. Thus, increased internet use during the lockdown in Spain was not related to a proportional growth in problematic usage, suggesting that these behavioral changes may constitute adaptive coping strategies in the context of the pandemic.