As the mobile networks are springing up, mobile devices become a must gadget in our daily life. People can easily access Internet application services anytime and anywhere via the hand-carried mobile devices. Most of modern mobile devices are equipped with a GPS module, which can help get the real-time location of the mobile device. In this paper, we propose a novel authentication scheme which exploits volatile passwords - One-Time Passwords (OTPs) based on the time and location information of the mobile device to transparently and securely authenticate users while accessing Internet services, such as online banking services and e-commerce transactions. Compared to a permanent password base scheme, an OTP based one can prevent users from being eavesdropped. In addition to a memoryless feature, the scheme restricts the validness of the OTP password not only in a certain time period but also in a tolerant geometric region to increase the security protection. However, if a legitimate user is not in the anticipated tolerant region, the user may fail to be authenticated. Hence, a Short Message Service (SMS) based mutual authentication mechanism is also proposed in the article to supplement the unexpected misjudgement. The proposed method with a volatile time/location-based password features more secure and more convenient for user authentication.