"He can stay as a guest and any request for asylum will be dealt with later," a Yemeni official said, adding that Ahmed was in the capital, Sanaa.
The website of President Ali Abdullah Saleh's ruling party said Yemen was hosting Ahmed as part of an accord between the governments of Yemen, Somalia and Kenya.
The agreement is part of "Yemen's efforts to achieve national reconciliation in Somalia and re-establish security and stability", a statement on the website said.
"Sheikh Sharif is a national Somali figure... who is convinced that dialogue is the best way of resolving the conflict in Somalia."
Some of his aides arrived in Yemen in early January, after the UIC was routed.
Since their defeat, the UIC have scattered to southern Somalia, and across to Kenya, some vowing a long guerrilla war.
Yemen, which has cracked down on Islamic hardliners in the country since the September 11 attacks, lies across the Gulf of Aden from Somalia and refugees often land on Yemeni shores.