The framing effect refers to the phenomenon that different descriptions of the same option lead to a shift in the choice of the decision maker. Several studies have found that emotional contexts irrelevant to a decision in progress still influence the framing effect on decision making. However, little is known about the potential role of emotional contexts in the framing effect on outcome evaluation under uncertainty and the related neural mechanisms. The present study measured event-related potentials (ERPs) to capture the time series of brain activities during the processing of gain- and loss-framed choices and outcomes primed with neutral and negative emotional contexts. The results revealed that in the neutral emotional context, the P300 amplitudes following both positive and negative feedback were greater in the gain-framed condition than those in the loss-framed condition, demonstrating a framing effect, whereas in the negative emotional context, this effect was unstable and observed only following negative feedback. In contrast, regardless of whether the feedback was positive or negative, the framing effect on the feedback-related negativity (FRN) amplitudes was insensitive to neutral and negative emotional contexts. Furthermore, the time-frequency analysis showed that the framing effect on the theta power related to the FRN was also insensitive to neutral and negative emotional contexts. Our findings suggest that brain responses to framing effects on outcome evaluation in a later cognitive appraisal stage of decision making under uncertainty may depend on the emotional context, as the effects were observed only following negative feedback in the negative emotional context.