The sitcom ran for four series from 2006 and while a fifth year was initially commissioned, creator Graham Linehan later said that it will not happen.
O'Dowd and Linehan had previously said that a fifth season would be the last and O'Dowd told Heat that he wanted some type of farewell.
"Well, the problem is that we've all ended up doing other stuff and being really busy, but I'd love to do something more with those characters," he said.
"I don't think we said goodbye to them properly. We need closure, as they say."
Asked if there would ever be a sequel to hit comedy Bridesmaids, he added: "I'd be surprised. I don't think those great people Kristen Wiig would do a sequel.
"I think they'll all work together again, those writers and actors, hopefully including me, but I doubt it'll just be a straight Bridesmaids sequel."
Watch Chris O'Dowd talk to Digital Spy about The IT Crowd below: