The Grecians have now moved up to third in League Two, for a few hours at least, while visiting Stanley have now won just one of their previous 16 matches.
The first half was a drab affair with the only highlight a long-range shot by Accrington's James Gray hitting the window of a house some 50 yards behind the Exeter goal.
Gray was equally as wasteful in the second half with another effort high and wide, but it was more than Exeter could muster as the hosts did not have an effort on goal until Keohane's opener.
The Irishman came on after 65 minutes and bagged his first 14 minutes later. It came after a clever one-two between Tommy Doherty and substitute Arron Davies, with the former having the presence of mind to lay the ball off to Keohane who finished with style.
Accrington almost levelled when Danny Coles sliced a clearance against his own crossbar, but the home side's second goal came from a dreadful back pass by Mark Hughes which gave Stanley goalkeeper Paul Rachubka plenty to do.
He was dispossessed by Jamie Cureton and Exeter's 18-goal top goalscorer laid the ball off to Keohane for an easy second.