In this paper, we performed an experiment with activated carbon manufactured from waste coffee grounds on the compressive strength of normal cement mortars. The activated carbon reinforcement was manufactured from waste coffee grounds, and the collected coffee grounds were then transformed into activated carbon granules through the physical activation process. The activated carbon/cement composites were prepared by mixing cement with activated carbon granules with the weight fractions of 0.5%, 1%, 1.5%, 5%, and 10% cement. The experimental results show that adding activated carbon up to 1.5 wt% increased the early strength of cement mortars. Furthermore, we found that the composites incorporated with a small amount of activated carbon (≤1.5 wt%) had higher compressive strength over the curing period than the normal cement without activated carbon. We believe that these results would potentially have commonalities with morphological symmetry phenomena that occur on the surfaces of activated carbon granules.