Baroness Paisley said in a statement that her husband was admitted to hospital on Saturday for some necessary tests.
"He is in good spirits.
"The family are grateful for those who have expressed concern and ask that his privacy be respected. There will be no further comment at this time."
The South Eastern Trust confirmed that he is being treated in the Ulster Hospital in Dundonald.
On Sunday afternoon, the deputy First Minister Martin McGuinness tweeted a get well message.
The post read: "Best wishes to Ian Paisley Snr, hopefully his stay in hospital will be short & he will soon be returned. home to his family in good health."
In February last year, Dr Paisley was admitted to the same hospital after suffering from heart problems.
He was treated in the intensive care unit for two weeks before being moved to the coronary care unit when his condition improved. During his spell of ill-health, he spent just over three weeks in hospital.
Dr Paisley became NI's First Minister when he was elected into power alongside Sinn Féin's Martin McGuinness in 2007.
He stepped down from political life in 2010. Last December, he preached his final sermon after standing down as moderator of the Free Presbyterian Church.
After retiring from both church and political life, he said he planned to write his autobiography.