The effect of specific cathode surface area (SCSA; 2, 4 and 8 m2/m3) on biogas production and biofouling control was investigated in anaerobic electrochemical membrane bioreactors (AnEMBRs). Nickel-based hollow fibers were used as both a cathode for hydrogen evolution and a membrane for the filtration of treated water. Varying the SCSA was found to influence the current density, biogas quantity and composition, and trans-membrane pressure (TMP). In situ gas generation was monitored using a high-speed camera; where the 8 m2/m3 AnEMBRs were found to mainly evolve smaller sized bubbles (45–114 µm) compared to the 2 and 4 m2/m3 AnEMBRs. This correlated with the lowest TMP (0.37 bars) compared to the other reactors (4 m2/m3, 0.76 bars; 2 m2/m3, 1.18 bars). The cathodic microbial community varied with SCSA, with Acetobacterium dominating at a relative abundance that reached 62% (4 m2/m3), while hydrogenotrophic methanogens (represented by Methanocorpusculum) comprised up to 2.5% of the total community. This community variability apparently influenced both the hydrogen (QH2) and methane (QCH4) production rates, reaching a maximum QH2 of 0.416 m3/m3/day (SCSA 8 m2/m3). Overall, this study discloses the cumulative effect of QH2, QCH4, bubble distribution and frequency on biofouling with SCSA variation in AnEMBRs, demonstrating that with higher SCSA the in situ gas scouring effect is more pronounced leading to a lower fouling propensity.