The patient is a man who became infected in Liberia and flew to Texas, where he is now being treated in hospital, a CDC spokesman told the AFP news agency.
He is not a healthcare worker, the spokesman added.
The Texas Health Presbyterian Hospital Dallas said earlier it had placed a person in strict isolation based on their “symptoms and recent travel history”.
CDC Director Doctor Thomas Frieden told a press conference US hospitals are well prepared to handle patients with Ebola, adding the virus should not pose the same threat in the US as it does in Africa.
“I have no doubt that we will control this importation of this case of Ebola so that it does not spread widely in this country,” he said.
Dr Frieden said he did not believe there is a threat to passengers on the same flight to the US as the patient, who did not display any symptoms when he left Liberia or upon entering the US.
He arrived in Texas on September 20 on a family visit.
The man sought treatment six days later and has been in hospital since the weekend.
Dr Frieden said this means he has potentially exposed a “handful” of family members and others to the virus.
President Barack Obama has been briefed by the CDC about the situation.
Twelve other people in the US have been tested for Ebola since July, with all of the results negative.
A handful of US medical workers who were infected in West Africa have been flown back to the US for treatment and have recovered.
Meanwhile, the British government has pledged a further £20m ($32.4m) to help the fight against Ebola in Sierra Leone.
It comes on top of the UK’s existing £100m ($162m) action plan, International Development Secretary Justine Greening announced.
An international conference is to be held in London on Friday to raise awareness of the disease and discuss how the global community can provide an effective response.
The current Ebola outbreak has infected 6,574 people across five countries and killed 3,091, according to the World Health Organisation.
