A Saudi official said at least two armed men stormed the office of the Saudi-owned company Rocky for Trade and Construction at 6.30pm (1530 GMT) on Tuesday and began shooting.
A spokeswoman for Ireland's Department of Foreign Affairs said she could not immediately comment on the report, but had since confirmed the death of Anthony Higgins.
It was the second killing of an Irish citizen by Saudi rebels in two months.
On 6 June, 36-year-old Simon Cumbers - a cameraman with the BBC - was shot and killed while videotaping a family home in Riyadh.
Various armed groups in the kingdom, such as the al-Haramain Brigades, criticise the government's relations with the West and are attempting to scare foreign workers into leaving the country.