Long-term motor deficits affect approximately two thirds of stroke survivors, reducing their quality of life. An effective rehabilitation therapy requires intense and repetitive training, which is resource demanding. Virtual Agents (VAs) and Socially Assistive Robots (SARs) offer high intensity, repetitive and reproducible therapy and are thus both promising as rehabilitation tools. In this paper, we compare a SAR and a VA during a rehabilitation task in terms of users’ engagement and movement performance, while leveraging neuroscientific methods to investigate potential differences at the neural level. Results show that our participants’ performance on the exercise was higher with a SAR than with a VA, which was especially clear under conditions of decreased perceptual information. Our participants reported higher levels of engagement with the SAR. Taken together, we provide evidence that SARs are a favorable alternative to VAs as rehabilitation tools.