The National Drug Law Enforcement Agency (NDLEA), which ordinarily targets drug traffickers, seized the currency and the 39-year-old woman as she tried to board a flight from Lagos to Congo-Kinshasa.
Officers at Lagos International Airport pulled over the woman, who comes from the Democratic Republic of Congo, after her plastic bag containing five dictionaries raised suspicions.
A search of the five reference books uncovered 24 brown envelopes, each containing USD 10,000 in USD 100 bills, the NDLEA said in an emailed statement. It added that the currency was suspected to be fake.
The woman was to be handed over to Nigeria's Economic and Financial Crimes Commission for further investigation and prosecution.
Nigeria's currency rules restrict the export of foreign currencies over USD 5,000. Any amount over that has to be declared upon departure.
Non-residents can export currency up to the amount imported and declared upon arrival.