Test anxiety poses a fundamental educational challenge as it is associated with lower academic performance and well-being. Grounded in the Self-Determination Theory, this study will focus on test anxiety fluctuations in relation to low-stakes assessments and investigates whether fluctuations in students’ experiences of autonomy and competence satisfaction and frustration relate to their test anxiety. For this purpose, 253 secondary school students completed a survey at three different times throughout the second semester. Students' feelings of autonomy and competence in the classroom were administered as well as their test anxiety. Each student completed the same two test anxiety scales at each measurement occasion, with one scale consistently administered to all students and the other two scales randomly assigned between classes. Multilevel analyses revealed that students showed higher test anxiety in weeks in which their need for competence was more frustrated and when they had to take more low-stakes tests. This association was robust across the three test anxiety instruments and after considering important test anxiety covariates (e.g., gender and prior achievement). These findings imply that competence frustration is an important underlying mechanism of test anxiety that should be taken into account when designing anxiety-reducing interventions.