Frontal alpha asymmetry has been proposed as a ubiquitous marker of state and trait approach motivation, but recent meta-analyses found weak or nonexistent links with personality traits. It has been suggested that frontal asymmetry may show stronger individual differences in situations that elicit approach motivation (state–trait interaction). To investigate this with sufficient statistical power, we utilized data from the CoScience project (N = 740). Frontal asymmetry was measured during a resting period, a picture viewing task, and a guessing task, which were expected to trigger different levels of approach motivation. Results showed that frontal asymmetry was not reliably affected by task manipulations and did not relate to self-reported traits. Furthermore, Bayesian statistics and a cooperative forking path analysis were used to supplement the preregistered analyses. To conclude, this comprehensive analysis could not support the validity of frontal asymmetry as a marker of approach motivation, neither as a reliable state nor as a trait marker.