This study investigates the development of composite materials tailored for high-efficiency electromagnetic shielding. The study focuses on incorporating rice bran biochar and cobalt particles alongside areca microfibers within a polyvinyl alcohol (PVA) matrix. The composites, fabricated via the solution casting process, underwent rigorous evaluation in accordance with relevant ASTM standards. Key findings include the remarkable relative permittivity values of PAB13, which achieved approximately 6.94, 4.92, 3.47, and 0.89 at 8, 12, 16, and 20 GHz; the successful outcome is ascribed to the strategic blend of 5.0 volume percent biochar and 2.0 volume percent cobalt particles. In contrast, PAB21 exhibited the lowest relative permittivity values, recording approximately 4.25, 2.35, 2.01, and 0.44 at the same frequencies. Moreover, PAB13 excelled in electromagnetic interference (EMI) shielding, with absorption values of around 14.44, 18.14, 44.12, and 46.81 dB, reflection values of about 3.13, 15.23, 12.43, and 17.02 dB, and total shielding effectiveness values of roughly 17.57, 33.37, 56.55, and 63.83 dB across 8 to 20 GHz frequencies. The study also revealed that PAB23 displayed exceptional magnetic permeability, exceeding other composites, with values of 3.6, 5.1, 6.1, and 12.1 at 8, 12, 16, and 20 GHz. This magnetic permeability superiority is attributed to its unique composition and the presence of 20 vol.% of areca microfibers, along with cobalt and rice bran biochar particles. Additionally, PAB22 showcased superior tensile strength, reaching up to 54.6 MPa, while PAB23 demonstrated the highest hardness values of approximately 44 Shore-D. These findings collectively emphasize the promise of these composite materials in high-efficiency shielding applications.