Yes you can, especially if you are used to it every year or you fast days like Mondays and Thursdays.

The Prophet (peace be upon him) said: “it is a month that deeds are brought up to God and I would like to be fasting during it.” (An-Nasa’i)

Only excluded from fasting of that month is the doubtful day which is the last day of Sha`ban one day before Ramadan.

It is better not to fast it unless it was a practiced habit. The Prophet (peace be upon him) said: “do not fast prior to Ramadan by a day or two except if a man was used on doing it.” (Al-Bukhari)