Health Secretary Paulyn Ubial said all 12 cases were locally transmitted, and that no other transmissions apart from mosquito bite has been recorded, Xinhua news agency reported.
"These cases did not have history of travel to an affected country a month prior to the onset of their illness," he said.
"All of these confirmed cases presented with skin rashes with any one of the following: fever, muscle or joint paints, conjunctivitis without eye discharge."
"All have recovered from their mild illness," the secretary said.
Ubial has ordered all health workers especially in regions where there are Zika cases to be more vigilant and to wage a more intensive mosquito control campaigns to eradicate mosquitos.
Zika virus is acquired through bites from infected Aedes aegypti mosquitos, the same type of mosquito that spreads dengue and chikungunya. Common symptoms include fever, skin rash, joint pains and conjunctivitis.