A deal is not imminent and could be reached in the first quarter, the source said, declining to be named because the talks are not public.
AlpInvest, which manages the private equity investments for Dutch asset managers APG and PGGM Investments, would help Carlyle diversify its businesses as it prepares to follow rivals Blackstone Group
Carlyle, one of the world's largest buyout firms with $97.7 billion under management and investments in companies such as Dunkin' Brands, has been considering an initial public offering for years and may file papers to go public late next year, a source previously told Reuters.
A sale of AlpInvest has been in the works for several months, according to media reports. APG and PGGM each own 50 percent of AlpInvest.
APG is the asset manager for ABP, the world's third-largest sovereign pension fund. PGGM is the asset manager for PFZW, the pension fund for the Dutch care and welfare sector.
Carlyle declined to comment on the news, which was first reported by Bloomberg. AlpInvest was not immediately available for comment.
(Reporting by Megan Davies; writing by Paritosh Bansal; Editing by Derek Caney)