The present study examined age-by-mood interactions in prospective memory and the potential role of attentional control. Positive, negative, or neutral mood was induced in young and older adults. Subsequent time-based prospective memory performance was tested, incorporating a measure of online attentional control shifts between the ongoing and the prospective memory task via time monitoring behavior. Mood impaired prospective memory in the young, but not older, adults. Moderated mediation analyses showed that mood effects in the young were mediated by changes in time monitoring. Results are discussed in relation to findings from the broader cognitive emotional aging literature.