The classic paradigm in finance maintains that asset returns are paid as a compensation for bearing risk. This study extends the literature and explores whether asset prices are also affected by uncertainty. This research invokes the Expected Utility with Uncertainty Probabilities Model and utilizes the natural experiment conditions of the COVID-19 pandemic outbreak, in order to determine whether investors’ behavior during the sharp economic decline was driven by risk, or uncertainty. We limit this research only to the outbreak of the pandemic, since the recovery of the markets suggests investors have adjusted to the unexpected nature of the crisis. Using high-frequency data of the S&P 500 Index, we estimate the investors’ risk and ambiguity aversions, finding that in the pre-pandemic period investors exhibited risk aversion as well as an ambiguity-seeking attitude, while during the pandemic they demonstrated risk- and ambiguity-neutral behavior. The implications of these findings could suggest that in regular times, the financial markets are operated by risk-averse investors with decreasing risk-averse behavior.