Fog computing is a new computing paradigm that has been proposed to extend cloud computing services to the edges of cloud computing networks. It has been proposed to support real-time latency-sensitive applications. Due to the far distance between end users and cloud data centers, fog computing has been introduced to reduce transmission latency and monetary cost of cloud resources. Task scheduling is a very essential issue in fog computing. Minimizing the total completion time of an application without violating user-defined deadline is one of the most important problems that is related to task scheduling in fog environments. In this paper, we have proposed a new algorithm called Deadline Aware Resource Allocation (DARA) algorithm. The main contribution of this algorithm is minimizing the completion time of applications, minimizing total cost of using resources and maximizing resource utilization under deadline constraints. The algorithm is compared with the DRAM algorithm, which focuses on load balancing and resource utilization without taking into consideration the overall completion time and user-defined deadline of tasks. Simulation results proved that our proposed algorithm provides better performance in terms of makespan, total cost, and resource utilization.