"Secretary Lew underscored that the commitments made by the G20 in Shanghai to use all policy tools ... to promote growth, refrain from competitive devaluation and not target exchange rates for competitive purposes," have contributed to confidence in the global economy in recent months, the Treasury Department said in a statement.
Lew and Aso met on Friday on the sidelines of the International Monetary Fund and World Bank meetings, reports Reuters.
In an earlier news conference on Friday, Lew said Washington "continued to emphasize the need" for countries to refrain from "begger-thy-neighbor" policies of attempting to weaken their currencies to revive their economies.
Japanese policymakers have frequently threatened to intervene in the currency market to stem sharp yen rises that could hurt exports. Washington has consistently warned Tokyo against intervening, branding such attempts as competitive devaluation.
In the news conference, Lew welcomed Japan's decision to postpone a second sales tax hike and compile a fiscal stimulus package to revive growth.