Access to the westbound carriageway at junction 41 has been blocked during morning and evening rush hours since August in a bid to ease congestion.
Transport Minister Edwina Hart said the trial suggested the benefits of partial closure could be worth Â£180,000 a year.
She said the restrictions would be lifted pending a decision whether to hold a full consultation on closures.
Local traders have complained that the twice-daily closures have hit their business.
But in a letter to assembly members on Friday, Mrs Hart said: "The trial has demonstrated a benefit to the M4 without overall dis-benefit to the local road network.
"The report also states that secondary measures including car parking, footfall, queue lengths and air quality did not show any significant impact attributable to the trial closure."
Peter Black, Liberal Democrat AM for South Wales West, welcomed the decision to end the trial closures but disputed the claim that there was no negative impact on Port Talbot town centre.
"I wonder whether the government officials carrying out this monitoring were in the right town," he said.
"Reading between the lines, I believe that the minister's statement has effectively kicked permanent closure of junction 41 into the long grass."
The slip road had been closed to traffic from 07:00-09:00 and 16:00-18:00 Monday to Friday.
A slip road on the M4 at Port Talbot is to fully reopen after trial closures but its future remains in doubt.