Jammeh has also said he will await a Supreme Court ruling in the case, delayed until January 10, before ceding power.
The Gambia's electoral commission building reopened on Thursday as the president said it had been shut for safety reasons rather than because of the country's disputed presidential vote result.
President Yahya Jammeh's political party has lodged a legal complaint against the Independent Electoral Commission (IEC) triggered in part by a vote recount in the days following a December 1 election, which ultimately confirmed opponent Adama Barrow's victory, 22 years after Jammeh took power.
The commission building was sealed off without warning by security forces on December 13, the same day the complaint to have the result annulled was lodged.
A decree issued late Wednesday claimed the authorities had received reports the IEC would be burnt down, stating: "Now that the threat has abated, the IEC head office will reopen."
The Gambia is facing prolonged political deadlock as Jammeh has said he will await a Supreme Court ruling in the case, delayed until January 10, before ceding power.
The president's stance has stoked international concerns about the future of the tiny west African country, with the UN joining African leaders in calling for him to step down.
IEC staff could return to work "with immediate effect", the statement added, but a visible security presence would be maintained around the compound close to the capital, Banjul.
The IEC's chairman Alieu Momar Njie confirmed to AFP the building had reopened but said work would resume Tuesday for staffing reasons and a public holiday on Monday.
"The Gambia Government made the announcement late Wednesday night and some of the staff were already in the rural area. This is why we did not go to work today, but we will go to work Tuesday morning," Njie said.
Court sources say six foreign judges have now been appointed by Jammeh to serve on the Supreme Court to hear his complaint, joining the sole sitting judge already on the bench.
The reopening of its headquarters will allow IEC officials time to prepare their case.
Meanwhile the decree also hit out at the tide of false news circulating on the internet and social media that claimed Jammeh had been deposed by his army chief.
"The Gambia under the leadership of His Excellency the President Sheikh Professor Alhaji Dr Yahya A.J.J. Jammeh Babili Mansa will continue to jealously guard the stability of the nation and ensure the maintenance of peace and security," the decree said.