Despite defeat to Grand Slam winners Wales last Saturday, O'Gara held on to top spot after amassing 60 points in the tournament, missing just seven of his 20 goal attempts.
Wales' Stephen Jones who, along with Jonny Wilkinson, is O'Gara's biggest challenger for a Lions' Test team spot this June, finished second with 22 successes for a 57-point return.
The award is some consolation to O'Gara, whose attempted clearance was charged down by prop Gethin Jenkins to set up Wales' 32-20 victory.
O'Gara told told Irish rugby website www.irishrugby.ie: "The charge-down try was a killer. I didn't see him and that made it 10-3, after we had started the game well.
"We were chasing the game from then on, but every time we got into a good position we gave away a penalty.
"But the better team won on the day."