The UK regulator has asked those advising on the £5.6bn deal to hand over any records, a Financial Times report revealed.
Investment bankers on the deal are also being asked whether they discussed the merger ahead of its announcement.
Sources have indicated that it is not uncommon for the FCA to investigate companies involved in large public takeovers, particularly if the deal is leaked prior to the formal announcement.
Aviva declined to comment.
In other news, it was announced today that the chief executive of Friends Provident International will move to Singapore-based insurer Great Eastern in October, after only a short period as FPI boss.