A brain-computer interface (BCI) is a system that conveys messages and commands directly from the human brain to a computer. The BCI system described in this work is based on P300 wave. The P300 is a positive peak of an event-related potential (ERP) that happens 300 ms after a stimulus. One of the most well-known and widely-used P300 applications is P300 speller designed by Farwell-Donchin in 1988. The Farwell-Donchin paradigm has been a benchmark in P300 BCI. In this paradigm, a 6x6 matrix of letters and numbers is displayed and subject focuses on a target character while rows and columns of characters flash. By detecting P300 for one row and one column, the target character can be identified. In this paper, it is shown that there is a human perceptual error in Farwell-Donchin paradigm. To remove this error, a new region-based paradigm is presented. Using experimental results, it is shown that the new paradigm has several advantages and it achieves a better accuracy compared to the Farwell-Donchin paradigm.