The commission had originally aimed to hold the conference at 8.30pm.
The EC's public relations department said the postponement was caused by some polling stations facing rains and flooding, thus preventing the officials from submitting the votes on time.
The press conference will be held at 10.30am on Monday, it added.
According to EC's Political and Electoral Development Institute as of 2.20am on Monday, 74.28% of 4.47 million people nationwide exercised their voting rights on Sunday. Of those counted, 3.19 million ballots are good, 48,694 ballots are void and 98,981 ballots are no votes.
Unofficial results at 2.20am showed Move Forward in the lead with 1.59 million votes, followed by United Thai Nation (628,938), Pheu Thai (598,776), Democrat (85,769), Thai Sang Thai (47,573), Chart Pattana Kla (46,123), Thai Liberal (42,829), Bhumjaithai (28,451), Palang Pracharath (22,033) and Thai Pakdee (14,039).