Multiprocessor Systems-on-Chip (MPSoCs) is a trend in VLSI design, since they minimize the "design crisis " (gap between silicon technology and actual SoC design capacity) and reduce the time to market. Important issues in MPSoC design are the communication infrastructure and task mapping. MPSoCs may employ NoCs to integrate multiple programmable processor cores, specialized memories, and other IPs in a scalable way. Applications running in MPSoCs execute a varying number of tasks simultaneously, and their number may exceed the available resources, requiring task mapping to be executed at runtime to meet real-time constraints. Most works in the literature present static MPSoC mapping solutions. Static mapping defines a fixed placement and scheduling, not appropriate for dynamic workloads. Task migration has also been proposed for use in MPSoCs, with the goal to relocate tasks when performance bottlenecks are identified. This work investigates the performance of mapping heuristics in NoC-based MPSoCs with dynamic workloads, targeting NoC congestion minimization, a key cost function to optimize the NoC performance. Here, tasks are mapped on the fly, according to communication requests and the load in the NoC links. Results show execution time and congestion reduction when congestion-aware mapping heuristics are employed.