Herein, we report a straightforward way to fabricate activated charcoal–magnetic nanocomposite (AC–MNC) by chemical precipitation for the sequestration of methylene blue (MB) from a simulated solution. The synthesised nanocomposite was characterised by Fourier transform infra-red (FTIR), Brunauer–Emmett–Teller (BET), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM) techniques. A good uniformity in the spherical AC–MNC particles is observed from a TEM image with an average particle size diameter of around 25 nm. AC–MNC possesses a specific surface area of 387.28 m2 g−1 with easy dispersibility and magnetic separation. The nanocomposite demonstrates an MB sequestration capacity of 147.71 mg g−1. The high efficiency of the nanocomposite is rationalised on the basis of H-bonding and electrostatic interaction between the electropositive N-atom of MB and electronegative oxygen-containing functional groups on the composite surface. Moreover, the exhausted AC–MNC can be efficiently regenerated by microwave irradiation followed by elution with methanol. The renewed nanocomposite showed good reusability. Thus, the synthesised AC–MNC proved to be an interesting and potential material for the remediation of MB-contaminated aqueous solution.