This paper deals with the ITEA (Information Technology for European Advancement) SmartTouch project whose one of the objectives is to use NFC mobile phones for a secure payment. An experience in real conditions has been carried out at Strasbourg in France, in 2007. This trial is the first experiment of a NFC-based payment application that fully supports the international EMV standard and the PayPass program. We focus in this paper on the security analysis which can occur in a NFC mobile phone payment. In the first section, we give a simplified description of the prototype. In the second section, we present the security concepts as a major issue in this scenario. Roughly, the main requirement is to have the same level of security as standard EMV payment transactions. The methodology described in the third section concerns the payment application and its communication with the payment terminal through a NFC link. The last part of this article presents different research perspectives to overstep the encountered problems.