Polyetheretherketone is a widely used engineering polymer that is especially suitable for high-temperature applications. Graphene is a two-dimensional form of carbon nanomaterial that has been studied extensively for its mechanical, electrical and thermal properties and its use as a filler in polymer matrices. Compounding graphene into polymers has the potential to improve various properties, even at very low concentrations. In this work, we have examined the incorporation of graphene nanoplatelets GnP and few-layer graphene into PEEK. We have fabricated composites using melt-mixing techniques, as well as by graphene functionalization and in-situ polymerization of the PEEK. In this way, we can compare the performance of the composites by two different composite fabrication methods. The composites were characterized by DSC, TGA, SEM, and mechanical properties as an adhesive in a lap-shear joint. In this work, we aim to produce a material that functions as a reusable high-temperature, thermoplastic adhesive, which can be activated by conventional heating methods, or by microwave heating. The GnPs act as microwave absorbers and heat the surrounding PEEK matrix to the point of melting, in contrast to the neat PEEK, which does not melt upon exposure to the microwaves under the same parameters. The microwave absorption properties and adhesive properties will be presented.