The Nasser Unionist People's Organization Party has said on its website that it had received anonymous messages threatening to assassinate Noaman, a staunch critic of the powerful Shiite Houthi group.
It also said that the sender accused Noaman, the party's secretary-general, of being an "agent" for foreign governments.
Noaman's party and most of Yemen's political forces had rejected last month's takeover of government institutions in capital Sanaa by the Houthi group.
Last week, Houthi militants prevented Noaman from boarding a plane from Sanaa to the southern Aden province, from which embattled President Abd Rabbuh Mansour Hadi is seeking to reinstate his rule.
Tension has been running high in Yemen since the Shiite Houthi group seized control of Sanaa in September and sought to extend its influence to other provinces.
Late last month, Hadi fled Sanaa, where he had been placed under house arrest by Houthis for weeks, to the southern Aden city and declared he was still Yemen's "legitimate" leader.
Upon his arrival to Aden, Hadi declared that all decisions taken by the Houthis since September were "null" and "illegitimate."