Care worker Alec Wallbank, 30, of Pontypridd, Rhondda Cynon Taff, is alleged to have carried out the offence between July and September 2014 in Cardiff.
He appeared at Cardiff Magistrates Court wearing a black shirt and tie.
He was released on bail and the case was sent to Cardiff Crown Court.
A plea and case management hearing is due to be held on 18 August.
A deputy manager of a mental health ward has appeared in court accused of engaging in sexual activity with a woman patient.