The ex-Latics striker snatched a 78th minute equaliser to cancel out Chris Porter's goal in the first half.
Beckett, who scored 18 times on loan for Oldham last season, almost joined the club on a permanent deal in July but instead ended up with their West Yorkshire rivals.
And Huddersfield were grateful as they dented Oldham's promotion bid as well as stretching their own unbeaten run to five matches.
Oldham made the brighter start and both Andy Liddell and Paul Warne blasted off target from the edge of the box.
Gary Taylor-Fletcher wasted a good chance for Huddersfield before the home side went in front on 23 minutes.
Warne flicked on a ball from defence and Porter chased it down before advancing into the Huddersfield penalty box.
He produced a well-struck finish into the far corner from 12 yards to celebrate his comeback from injury and make it 21 goals for the season.
Warne almost added a second but Huddersfield got back on equal terms in the second half after changing their system to 4-4-2.
Martin McIntosh headed over before Oldham squandered two opportunities to double the lead through Porter and Warne.
The visitors punished those misses when young substitute James Berrett headed down a cross and Beckett stooped at the far post to convert at close range.
Huddersfield could have grabbed another when Jon Worthington broke into the box but his shot was tipped over by Australian keeper Les Pogliacomi.