You want to cast the field to be a numeric value instead, so that MySQL will order it with a numeric comparison, rather than a string comparison.
SELECT your_column
FROM your_table
ORDER BY CAST(your_column AS DECIMAL) ASC
The above will work with negative numbers too, if you have any of those in your table.
Although if the field only contains numeric data, you really should be storing it as such, rather than as a varchar. Having a cast in your query will dramatically affect performance as you get more rows.