I am going to buy audio interface which won't have a midi input so my question is are there some adapters that can let me plug midi keyboard to this audio interface?
Directly to the audio interface probably not.
However, there is a lot of MIDI to USB adapters that exists in the market. As I assume your audio interface will be connected to a computer with USB, that would be the way to go.
To get Midi to your computer, you'll need a separate Midi-USB interface. The most frequent offer you'll find on auction sites is some variant of a cheap Chinese interface with a stylised mixture of treble and bass clef on it. This interface will garble polyphony and SysEx messages. It may also cause noise in the audio path when connecting keyboard and computer using both audio and Midi.
Ancient interfaces (USB1.1 fullspeed at 12Mbps is fast enough given good chipsets for encapsulating the 31.250kbps Midi stream) from reputed manufacturers will work and there is an increasing amount of proper reasonably affordable newer offers (products with chips from Ploytec work convincingly in my experience). The review sections from actual music stores might be somewhat more reliable than what you see elsewhere on the Internet, but one still needs to carefully peruse the more thorough reviews when checking items of the "appears to work when looking superficially" kind: the score itself tends to end up higher than often called for.
If your MIDI keyboard is an older one with only the 5-pin MIDI connectors, it will need an interface to your computer. Some audio interfaces have one built-in. If you choose one that hasn't, you'll need a separate one. (Note that the job is interfacing the keyboard to your computer, not interfacing it to the audio device.)
You won't have to pay a lot, but avoid the VERY cheap ones that can be found on eBay.
Check that the keyboard doesn't also have a MIDI-over-USB connector. This would plug straight to the computer, making a separate interface unnecessary.