Analysts say Mr Jobs will likely start back at work on a part-time basis
Apple chief executive Steve Jobs has reportedly returned to work following six months of medical leave.
Mr Jobs, 54, who is reported to have had a liver transplant, was expected back at his desk at the end of June.
Apple has refused to comment on the matter but did quote Mr Jobs in a press release on first weekend sales figures for the next generation of iPhones.
The blogosphere has noted several sightings of Apple's co-founder around its campus in Silicon Valley.
"Jobs is in the house!" declared CNBC's Jim Goldman, who is regarded as having close ties to Apple.
"Confirmed! Steve Jobs did report for work today, according to employees who have seen him on campus," wrote Mr Goldman in his TechCheck column.
Reuters news agency quoted sources saying Mr Jobs "was seen leaving the main Apple building in Cupertino and getting into a black car alone that was driven off by men in black suits with ear-pieces."
In 2004, Mr Jobs was treated for pancreatic cancer.
Last year there were fears that the cancer had returned when he appeared at a major Apple event looking thin and gaunt.
Months of rumour ensued and the company's share price rose and fell as a result.
In January, Mr Jobs revealed that he was being treated for a "hormone imbalance".
Over a week later he sent an e-mail to employees and told them that his medical problems were more complex than first thought and he would take six months off work to concentrate on his health.
The Wall Street Journal reported over the weekend that Mr Jobs underwent a liver transplant over two months ago, but Apple remained tight-lipped on the subject.
Analysts have predicted that Mr Jobs will stay on as chief executive officer on a part-time basis with a view to moving on to become chairman of the company.