In this study, a mediator-free glucose/$O_2$ biofuel cell was developed based on a 3-dimensional carbon nanomaterial/polypyrrole composite with glucose oxidase and tyrosinase as the anodic and cathodic catalysts, respectively. This mediator-free biofuel cell has the following merits: (1) the biocatalyst was unaffected by toxic mediators and (2) current generation is independent, because there is no problem associated with mediator leakage from the electrode. The carbon nanomaterial in this 3-dimensional composite was used not only as immobilization support for the biocatalyst, but also as an electron carrier. This would be advantageous for glucose oxidation on the bioanode and $O_2$ reduction on the biocathode in the glucose/$O_2$ biofuel cell. This biofuel cell showed enhanced power density and half-life compared to other glucose/$O_2$ biofuel cells previously reported, producing 157.4 ${mu}W/cm^3$ with 1 mM glucose as fuel and 0.5 M NaCl as the electrolyte, at a cell voltage of +85 mV over 29 h with continuous 1 mM glucose feeding.