The correlation observed between the Li abundance and surface activity of young cool stars is not explained by current stellar evolution models. We study the possibility that this correlation arises from significant in situ production of Li by solar-like flares. Using the X-ray luminosity of the stars as an indicator of their surface activity, we show from a comparison of the Pleiades and Hyades clusters that Li production by flares cannot account for all the dispersion in Li abundance observed in young open clusters. Stellar flare nucleosynthesis might explain, however, unexpected detections of Li in several M-type dwarfs.