A dynamic membrane was formed by introducing powder-activated carbon (PAC) prior to the cross-flow microfiltration of seawater. The microbes and organic matter in the seawater were removed efficiently through the interception, adsorption, and biodegradation of the PAC dynamic membrane. The properties of PAC dynamic membranes formed under various operating conditions were analyzed. The relationship between the specific filtration resistance of a dynamic membrane and transmembrane pressure was regressed as a power-type empirical equation for a given cross-flow velocity. An increase in cross-flow velocity led to higher specific filtration resistance because of the smaller particle size distribution. The thickness of a dynamic membrane increased with the transmembrane pressure but decreased with the cross-flow velocity. The thickness was correlated with the ratio of tangential to normal drag forces exerted on the PAC particles on the membrane surface. The filtrate quality for PAC dynamic membrane filtration was analyzed. Humic acid (HA) and turbidity were not detected. The chemical oxygen demand (COD) and dissolved organic carbon (DOC) had maximum removals of approximately 80% and 92%, respectively. The behavior by which HA was adsorbed on a PAC conformed to the Freundlich isotherm, and the modified Wheeler equation produced appropriate estimates of the breakthrough time. The breakthrough time increased with the thickness of the dynamic membrane. This study presents a method by which the filtration performance, such as filtration flux, thickness, and breakthrough time of the dynamic membrane, can be predicted directly from operating conditions.