I'm a Filipino citizen, and I am in Macau. Can I get visa upon arrival in South Korea (Seoul)?
The Philippines is not amongst the Countries under visa exemption agreement for ordinary people. Its citizens are, however, exempted of visa fees for short stay of no more than 59 days.
So, as far as I can tell, the answer to your question is no. You have to apply for a visa before coming to South Korea.
See also: Wikipedia: Visa policy of South Korea