Younger adults consistently outperform older adults in laboratory prospective memory tasks. This study examines the effectiveness of an intervention that familiarizes older adults with the sequence of ongoing events to compensate their reduced prospective memory performance. We compared performance and electrophysiological measures of an intervention group (N = 20, 69-83 years) receiving a familiarization intervention to an individually matched control group (N = 20). As ongoing activity a 2-back working memory task was administered. Neural correlates were studied using event related potentials (ERPs) and source localization (standardized low-resolution brain electromagnetic tomography). Behavioural data showed faster reaction times in correct prospective trials and fewer prospective false alarms in the familiarization intervention group. ERP analyses displayed differential patterns for the two groups and source localization measures distinctively presented group differences in prospective memory trials with the control group recruiting more resources for a successful prospective memory performance. Together our data support the hypothesis that the familiarity with the sequence of ongoing events increases prospective memory performance and that this might be based on a higher efficiency of attentional monitoring resources and evaluation processes in the intervention group.