Biomagnetic responses were recorded from healthy elderly subjects (55-67 years) performing a working memory task during recognition. The objective was to identify differential spatio-temporal brain activity patterns with magnetoencephalography by the presentation of two types of retroactive interference, active and passive. We obtained increased activity in the left medial temporal lobe and the left anterior ventral prefrontal cortex at early (100-200 ms) and medium latencies (300-400 ms) for the active interference group, and left anterior ventral prefrontal cortex showed greater activity at late latencies (700-800 ms) for the passive interference group. A time-modulated ventral prefrontal activation was shown for the active and passive interference conditions indicating that executive control mechanisms were necessary in both groups.