The Dutchman came through the youth ranks at Manchester City and went on to join Celtic in September 2019 before a move to Leverkusen in January 2021.
Frimpong joins a Dutch contingent of Virgil van Dijk, Cody Gakpo and Ryan Gravenberch at Liverpool.
Liverpool are also in talks with Leverkusen over signing Florian Wirtz.
The club have entered into advanced negotiations for Germany forward Wirtz, submitting an offer of around £109m inclusive of add-ons.
Wirtz, 22, is a key target for Liverpool and there is now a sense that discussions over a deal are in its final stages, with a growing hope an agreement is within reach.
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