He said it was "all very personal and undignified so I might as well bite the bullet", before explaining that he had seen his doctor in December in order to get a flu jab, but that it was discovered that he had cancer.
"It doesnt seem to have spread, because what you dont want is to spread from one area to another, but one of the lymph nodes had something that called for active surveillance".
Fry said he was shocked when he found out he had cancer.
He also encouraged men to have routine prostate exams.
Stephen added: "So, what next, well you have to recover and that's what I've been doing really in case you've been wondering why I've been out of the public eye".
"Here's hoping I get another few years on this planet because I enjoy life at the moment and that's a marvellous thing to be able to say - and I would rather it didn't go away".
The prostate-specific antigen (PSA) test, via a blood sample, is used to help diagnose prostate cancer. The 60-year-old actor, who stepped down last month as Bafta film awards presenter, shared details about his illness in a video on Twitter.
"But if there's anything left on the bed of the prostate where they've taken it out, it may have spread and I'll have to get radiotherapy and the whole damn thing will start again".
He said: "For the moment, I'm fit and well and happy and I just wanted to let you know". Are there greater chances of me getting other kinds of cancer now? I wasn't being examined for anything as beastly as Satan, but something as beastly and it was in the prostate that they were looking at. Please know you're not alone, and that talking openly and honestly about your experiences is very fearless.
Fry, who has previously appeared on Irish soap opera Ros na Rún, said he life was saved by the early intervention.