COVID-19 pandemic has impacted all facets of society, including students, as daily learning activities were severely affected while the face-to-face classes were forced to be held online. As a result, students underwent tremendous stress and were exposed to severe mental health conditions. Thus, this study investigates how the integration of casual video games into online learning can relieve stress among science students. An online survey was designed and disseminated to students via social media. The respondents were pre-assessed for stress and emotional conditions during their online learning. Then, the respondents were instructed to watch a tutorial video from YouTube and play a quiz-like casual video game that we had developed. The respondents were then reassessed for stress and emotional level (post-assessment) to understand how casual video games can relieve their anxiety in online learning. All questionnaires in this survey were tested for the Likert scale, with one being strongly disagreed and five strongly agreed. Similar pre-and post-survey questionnaires were designed and tested against academicians for their perceived efficiency of casual video games in online learning. The outcome from this study has shown significant improvements in students' stress and mental emotional levels when casual video game is introduced as part of their online lesson. On the other hand, the academicians perceived that online teaching alone is as effective as casual video games during online learning. However, the academicians also perceived that casual video games could significantly reduce students' stress and emotional during online classes. We propose that casual video games are considered an integral tool for online teaching and learning as they can significantly reduce students' stress in online learning during the Covid-19 lockdown.