Rahmani's first feature-length production received the event's Best Children's Feature Film award.
The Other depicts the relationship between a boy and man, who is soon to become his stepfather.
Produced by Mohammad Ali Najafi and Shafi Agha Mohammadian, the film has also won the World Premiere Prize of the 2010 International Avanca Film Festival held in Portugal.
The 2010 APSA's Best Feature Film prize went to Chinese director Feng Xiaogang's Aftershock, while the Best Animated Feature Film and Best Documentary Feature Film prizes were granted to China's Piercing and Last Train Home respectively.
This year's films were judged by Tannishtha Chatterjee (India), Ellery Ryan (Australia), Salman Aristo (Indonesia), Ming Zhenjiang (China), Sergey Dvortsevoy (Kazakhstan), Serdar Akar (Turkey) and Lord David Puttnam (UK), who led the board of jury.
Award-winning Iranian filmmaker Asqar Farhadi also received a USD 25,000 grant from the Motion Picture Association and APSA for the script development of his next project Nader and Simin: A Separation.
The film was assessed as "a beautiful human study of a very normal everyday life, with people in a region who are being challenged all the time by issues social, geographical and financial."
Farhadi won last year's Best Screenplay and the Jury Grand APSA awards for his About Elly.
The Asia Pacific Screen Awards is a collaboration involving CNN International, UNESCO and the FIAPF - International Federation of Film Producers Associations.