Permission for the export, worth more than $130 million, was granted by the country's Council of State.
Under the order from General Dynamics, Patria send General Dynamics Land Systems 36 Nemo systems together with 1,440 ammunition storage tubes and spare parts.
Deliveries will take place in 2012 and 2013.
Patria said it delivered six systems to General Dynamics earlier this year for testing.
"Obtaining an export license is a major step forward for this technology," said Patria Land Services President Seppo Seppala.
"It is also an important waypoint in efforts to market Finnish mortar systems internationally."
NEMO is a 122mm turreted system for land as well as maritime use.
The Council of State is made up of the government's Cabinet ministers. Four voted against granting export license, citing what they said were Saudi Arabia's human rights violations and political system.
The government of Finland is the majority shareholder in Patria.