The arrangement of letters on a keyboard greatly influences the user's comfort and typing speed. With repetitive muscular injuries emerging and the amount of text to be treated increasing, the need for a better arrangement has come forth. To solve the problem, a non-trivial abstract representation of a physical keyboard layout and of type-writing rules is introduced. Having justified the choice of heuristic ergonomic criteria, a mathematical function for the ergonomic evaluation criteria is developed. Based on the ant colony optimization algorithm, an optimization algorithm is designed and applied to the problem described. The computational results representing the quality of the keyboard arrangements obtained for several languages are finally discussed and new solutions for optimization of the keyboard are presented.