Peace be upon you. It is permissible to uncover your hair in front of your uncle, as he is considered one of the close relatives (mahram). According to Ayatollah Khamenei and Ayatollah Sistani, it is prohibited to reveal oneself to a niece, whether through paternal or maternal lineage. However, since your uncle is a close relative, revealing your hair in front of him is allowed. May you be successful in all good deeds.