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Background Physical activity (PA) has been identified as one of the most relevant modifiable lifestyle factors against Alzheimer's disease (AD). Magnetoencephalography has proven to be a useful tool to predict future risk of AD. In particular, decreased power in the alpha band has been associated with pathological aging. We had already reported how PA was significantly associated with higher alpha peak frequencies in older adults, especially among those at standard genetic risk for AD (APOE ε4 non‐carriers). Recent literature suggest that age could play an important role in the emergence of these relationships, a role that has not been explored yet. Method We used a sample of 112 cognitively normal individuals aging <50 who had worn an accelerometer for one week, divided into four carefully matched groups: younger adults at increased risk (age <60;APOE ε3ε4;n=20), older adults at increased risk (age >60;APOE ε3ε4;n=15), younger adults at standard risk (age <60;APOE ε3ε3;n=44) and older adults at standard risk (age>60;APOE ε3ε3;n=33). Each subject underwent four minutes of closed eyes resting state MEG recording. The aim was to detect any robust correlation between power values derived from clusters of nodes localized in certain brain regions and TPA, using network‐based statistics. Clusters consisted of several adjacent nodes, which systematically showed a significant partial correlation (with age as covariate) in at least 3 consecutive frequency steps between their corresponding power values and TPA (spearman correlation p‐value<0.01). Result A significant cluster was found in the frequency interval 10.75–13Hz involving mainly posterior brain regions (rho=0.360;p=0.0001;see Figure 1/Table 1). This correlation remained significant for both ε3ε3 carriers (rho=0.326;p=0.004;n=77;) and ε3ε4 carriers (rho=0.442;p=0.007;n=35;see Figure 2). It also remained significant for younger adults (rho=0.456;p>0.001) but not for older adults (Figure 3). Interestingly, when looking at the four groups individually, only younger ε4 non‐carriers (rho=0.487;p>0.001) and older ε4 carriers (rho=0.603;p=0.013) show this association. Conclusion Greater PA seems to be associated with increased alpha power in posterior brain regions, a robust biomarker of brain health which is negatively affected in AD. However, the time window when this association can be observed seems to differ between ε4 carriers and non‐carriers.