This paper presents online estimation framework of a cognitive performance using heart rate variability (HRV). Although our former framework could estimate relative changes in one user\'s cognitive performance after it had finished measuring his/her HRV, it was unable to estimate a cognitive performance repeatedly or to compare the estimated results obtained for multiple users. To address these problems, we have developed a framework for online estimation of a cognitive performance. Experimental results show our framework estimates a cognitive performance more accurately than the previous study did using multiple vital sensors. It can also estimate a user\'s cognitive performance by comparing it with those estimated for others. It therefore has the potential to help managerial personnel monitor their workers\' performances in real time to suggest rest periods or changes in work duties.