<PAGE>
 
                                                                      Exhibit 11
                                                                      ----------
               BOSTON COMMUNICATIONS GROUP, INC. AND SUBSIDIARIES
                STATEMENT RE: COMPUTATION OF PER SHARE EARNINGS
                   (In thousands, except for per share data)
                                  (Unaudited)


<TABLE> 
<CAPTION> 
                                       Three months ended  Nine months ended
                                       September 30,       September 30,
                                       1996       1997     1996     1997
                                       ----       ----     ----     ----
NET INCOME PER COMMON SHARE - PRIMARY
<S>                                    <C>      <C>      <C>      <C>
Net income                             $   331  $   101  $   453  $   237
                                       =======  =======  =======  =======
                                    
Primary income per share:           
Average common shares outstanding       12,587   14,372    6,864   13,284
Dilutive options and warrants              524      774      524      483
Other (1)                                    -        -    3,205        -
                                       -------  -------  -------  -------
                                    
Average common and common           
 equivalent shares outstanding          13,111   15,146   10,593   13,767
                                       =======  =======  =======  =======
                                    
Net income per common               
 share - Primary                       $  0.03  $  0.01  $  0.04  $  0.02
                                       =======  =======  =======  =======
 
<CAPTION>  
NET INCOME PER COMMON SHARE - FULL DILUTION
<S>                                    <C>      <C>      <C>      <C>
Net income                             $   331  $   101  $   453  $   237
                                       =======  =======  =======  =======
                                    
Fully diluted income per share:     
Average common shares outstanding       12,587   14,372    6,872   13,284
Dilutive options and warrants              548      782      548      611
Other (1)                                    -        -    3,205        -
                                       -------  -------  -------  -------
                                    
Average common and common           
 equivalent shares outstanding          13,135   15,154   10,601   13,895
                                       =======  =======  =======  =======
                                    
Net income per common               
 share - Full Dilution                 $  0.03  $  0.01  $  0.04  $  0.02
                                       =======  =======  =======  =======
</TABLE>

(1)Pursuant to Securities and Exchange Commission Staff Accounting Bulletin No.
83, Common Stock and stock options issued during the twelve-month period
preceding the date of the initial filing of the registration statement with an
exercise price below the initial public offering price of $14.00 per share have
been included in the calculation of common equivalent shares, using the Treasury
stock method, as if they were outstanding for all periods presented.