The MACC arrested an engineering consultant who was involved in the preparation of the feasibility study of the Penang tunnel project.
She was arrested after presenting herself at the MACC headquarters in Putrajaya at 6.10pm.
MACC deputy commissioner (operations) Azam Baki, when contacted, confirmed the arrest.
According to a source, the woman, who is in her 50s, was allegedly involved in the preparation of fake claims for the RM305 million feasibility study.
The MACC is also investigating whether she was involved in the forgery of documents.
She is the third person to be arrested in relation to the project following the detention of two "datuks" from separate companies of Jan 10.
Both have been freed on RM200,000 bail each.