Permanent secretary for public health Narong Sahametapat said on Tuesday the 24-year-old woman recently returned to Thailand from Guinea, a centre of the Ebola outbreak, and had developed symptoms that indicate she could be infected by the deadly virus.
Sopon Mekthon, director-general for the Department of Disease Control (DDC), said the woman, whose name was not disclosed, had a high fever, at 38.8 celsius, sore throat and runny nose.
The case was reported to the ministry on Monday and the woman is being kept separate from other people under care at a state hospital.
A blood sample was tested by the Department of Medical Sciences and Chulalongkorn Hospital on Tuesday and another sample would be tested on Thursday for accuracy, Dr Sopon said. The patient's condition was improving.
The ministry did not release the result of the first test.
A surveillance and rapid response team of the DDC has found 16 people who had been in contact with the patient, and none of them showed any sign of the disease, he added.
All would be monitored for 21 days, in line with Ebola surveillance measures.
The deadly virus has killed a confirmed 1,546 people in West Africa, according to the World Health Organisation. The outbreak is centred on Guinea, Liberia, Nigeria and Sierra Leone.
The ministry cleared another woman on Aug 22 after monitoring her for suspected Ebola infection. Her blood tests proved negative. The woman had worked in Liberia and returned to Thailand on Aug 20.