There is a keyboard and mouse adapter for the playstation 2 console:

PS2 Max Shooter (Smart Joy Frag) Keyboard and Mouse Adapter

Now you have total control on your PS2. No more wishing you had PC accessories while playing your favorite PS2 1st person shooters!

Features:

• Connect PC Mouse and Keyboard to your PlayStation 2
• Especially designed for First Person Shooters
• PC-based comfort and acclaimed gameplay now on PlayStation 2
• Supports all keys on Keyboard and Mouse (including Scroll-Wheel)
• Pre-Installed configurations for most FPS Best Sellers
• Fully programmable including advanced features such as Deadzone and Mouse Control Inversion
• Works with any game, even without built-in Mouse + Keyboard support
• Compatible with all PlayStation®2 consoles (US, JPN, PAL)
• Compatible with standard PS/2 Mice, incl. USB Mice with a USB to PS/2 Adapter
• Compatible with Optical and Wireless Mice

see the attached image


I am guessing this is the one you have, if not, search for PS2 Max Shooter (Smart Joy Frag) Keyboard and Mouse Adapter on google