Just like mp3, ogg is a lossy format, so yes, just as if you reencoded your mp3 into mp3 (even at the same bitrate) you would lose a bit of quality, you will lose something with an mp3-ogg conversion, but it should be minimal. Ideally you'd convert from CD directly to ogg. Then at the same bitrate as your MP3 ogg should actually sound better because it uses variable bitrate, so if it needs a bit more than 192k it uses it, while during a particularly easy to compress section of the song it may choose to use less than 192k (eg. silence at 1k, or 192k is still silence)
Read this for more info
http://www.vorbis.com/faq.psp#lossy