Continuous monitoring of mental workload offers new opportunities to support preventing mental disorders and maintaining mental health. In order to achieve a quantification of mental workload, different load levels have to be discriminated. This work goes towards continuous monitoring of mental workload in daily life: we present our experimental designs and the achieved results in discriminating three levels of mental workload in a laboratory simulation and in daily life. In the lab setting we achieved an average recognition rate of 82.14% for all 7 subjects under study. In daily life two subjects were monitored during low, medium and high workload days. We achieved average accuracy rates of 72.03% and 77.66% for both subjects respectively. Finally we have investigated whether the data from the lab experiment are suitable to discriminate low, medium and high workload days.