This study investigates the dielectric relaxations of an unsaturated polyester matrix (PS) reinforced with varying weight fractions of argan nutshell powder (ANS) as a biofiller across temperatures ranging from 303 K to 453 K and frequencies from 0.1 Hz to 1 MHz. At low temperatures and high frequencies, dielectric relaxations are primarily attributed to the dipolar polarization of water associated with argan nutshell powder (ANS) charges. As temperatures increase and within the intermediate frequency range, dielectric relaxations are attributed to the α-relaxation process resulting from the rubbery glass transition of the polyester matrix (PS). Beyond the glass transition temperature and at low frequencies, dielectric relaxations are associated with the interfacial polarization effect, arising from the accumulation of charges at the interfaces between the filler and the matrix. Filler/matrix interactions are further examined in terms of the interfacial polarization effect, with consideration given to the increase in the weight fraction of the argan nutshell powder (ANS). Additionally, this study elucidates the impact of filler/matrix interactions on the dielectric properties of the composite system, offering valuable insights into the role of argan nutshell powder (ANS) as a biofiller in enhancing the performance and functionality of an unsaturated polyester matrix (PS) for potential applications in materials engineering.