Modern Network Intrsuion Detection Systems (NIDSs) use anomaly detection to capture malicious attacks. Since such connections are described by large set of dimensions, processing these huge amounts of network data becomes extremely slow. To solve this time-efficiency problem, statistical methods like Principal Component Analysis (PCA) can be used to reduce the dimensionality of the network data. In this paper, we design and implement an efficient FPGA architecture for Principal Component Analysis to be used in NIDSs. Moreover, using representative network intrusion traces, we show that our architecture correctly classifies attacks with detection rates exceeding 99.9% and false alarm rates as low as 1.95%. Our implementation on a Xilinx Virtex-II Pro FPGA platform provides a core throughput of up to 24.72 Gbps, clocking at a frequency of 96.56 MHz.